Taipei 101

Taipei 101 (stylized in all caps), formerly known as the Taipei World Financial Center, is a skyscraper in the capital Taipei, Taiwan. It is owned by Taipei Financial Center Corporation. The building was officially classified as the world's tallest from its opening on 31 December 2004 (in time to celebrate New Year's Eve). However, the Burj Khalifa surpassed Taipei 101 in 2009. Upon completion, it became the world's first skyscraper to exceed a height of half a kilometer (about 0.3 miles). As of 2023, Taipei 101 is the tallest building in Taiwan and the eleventh tallest building in the world.
The elevators of Taipei 101 that transport passengers from the 5th to the 89th floor in 37 seconds (attaining ) set speed records. In 2011, Taipei 101 was awarded a Platinum certificate rating under the LEED certification system for energy efficiency and environmental design, becoming the tallest and largest green building in the world. The structure regularly appears as an icon of Taipei in international media, and the Taipei 101 fireworks displays are a regular feature of New Year's Eve broadcasts and celebrations.
Taipei 101's postmodernist architectural style evokes traditional Asian aesthetics in a modern structure employing industrial materials. Its design incorporates a number of features that enable the structure to withstand the Pacific Ring of Fire's earthquakes and the region's tropical storms. The tower houses offices, restaurants, shops, and indoor and outdoor observatories. The tower is adjoined by a multilevel shopping mall that has the world's largest ruyi symbol as an exterior feature.
History
Development
In 1997, led by developer Harace Lin, the Taipei Financial Center Corporation, a team lead by several Taiwan banks and insurance companies, won the rights to lease the site for 70 years and develop a building, placing the winning bid of NT$20,688,890,000 for the Build Operate Transfer agreement with the city government. The property will return to the city in 2067.
The Taipei Financial Center Corporation (TFCC) announced plans on 2 November 2009 to make Taipei 101 "the world's tallest green building" by summer of 2011 as measured by LEED standards. The structure is already designed to be energy-efficient, with double-pane windows blocking external heat by 50 percent and recycled water meeting 20–30 percent of the building's needs. LEED certification would entail inspections and upgrades in wiring, water and lighting equipment at a cost of NT$60 million (US$1.8 million). Estimates show the savings resulting from the modifications would pay for the cost of making them within three years. The project was carried out under the guidance of an international team composed of Siemens Building Technologies, architect and interior designer Steven Leach Group and the LEED advisory firm EcoTech International. The company applied for a platinum-degree certification with LEED in early 2011. On 28 July 2011, Taipei 101 received LEED platinum certification under "Existing Buildings: Operations and Maintenance". It replaced the Bank of America Tower in Manhattan as the world's tallest and highest-use green building in addition to the Environmental Protection Agency building in Florida as the world's largest green building. Although the project cost NT$60 million (US$2.08 million), it is expected to save 14.4 million kilowatt-hours of electricity, or an 18 percent energy-saving, equivalent to NT$36 million (US$1.2 million) in energy costs each year. In 2012, the shopping center at the base is expected to be remodeled. In 2019, it was named among the 50 most influential skyscrapers in the world by the Council on Tall Buildings and Urban Habitat.
On 4 January 2020, the building had a condolence message in lights for the victims of a helicopter crash, which included a number of senior government officials. On 8 February 2020, the press said that some passengers of the Diamond Princess cruise liner, quarantined for an outbreak of COVID-19, had visited Taipei 101 on 31 January at which point none exhibited symptoms. On 1 April 2020, the Taipei 101 shopping center said it was reducing business hours due to the Coronavirus pandemic, making the "nation's first to cut back operations due to the pandemic." It had started checking shopper's temperatures in February. On 21 May the building said it would resume normal business hours in June, as the country had effectively limited the spread of COVID-19.
Timeline
Important dates in the planning and construction of Taipei 101 include:
Construction
Planning for Taipei 101 began in July 1997 during Chen Shui-bian's term as Taipei mayor. Talks between merchants and city government officials initially centered on a proposal for a 66-story tower to serve as an anchor for new development in Taipei's 101 business district. Planners were considering taking the new structure to a more ambitious height only after an expat suggested it, along with many of the other features used in the design of the building. It was not until the summer of 2001 that the city granted a license for the construction of a 101-story tower on the site. In the meantime, construction proceeded and the first tower column was erected in the summer of 2000.
A major earthquake took place in Taiwan during 31 March 2002 destroying a construction crane at the rooftop, which was at floor number 56. The crane fell down onto the Xinyi Road beneath the tower, crushing several vehicles and causing five deaths - two crane operators and three workers who were not properly harnessed. However, an inspection showed no structural damage to the building, and construction work was able to restart within a week.
Taipei 101's roof was completed three years later on 1 July 2003. Ma Ying-jeou, in his first term as Taipei mayor, fastened a golden bolt to signify the achievement. The formal opening of the tower took place on New Year's Eve 2004. President Chen Shui-bian, Taipei Mayor Ma Ying-jeou and Legislative Speaker Wang Jin-pyng cut the ribbon. Open-air concerts featured a number of popular performers, including singers A-Mei and Stefanie Sun. Visitors rode the elevators to the Observatory for the first time. A few hours later the first fireworks show at Taipei 101 heralded the arrival of a new year.
Usages
Events and celebrity appearances
Taipei 101 is the site of many special events. Art exhibits, as noted above, regularly take place in the Observatory. A few noteworthy dates since the tower's opening include these below:
On 28 February 2005, former President of the United States Bill Clinton visited and signed copies of his autobiography. On 19 April 2005, the tower displayed the formula "E=mc2" in lights to celebrate the 100th anniversary of the publication of Einstein's theory of relativity. The display, the largest of 65,000 such displays in 47 countries, was part of the international celebration Physics Enlightens the World. On 20 October 2006, the tower displayed a pink ribbon in lights to promote breast cancer awareness. The ten-day campaign was sponsored by Taipei 101's ownership and Estée Lauder.
On 25 December 2004, French rock and urban climber Alain Robert made an authorized climb to the top of the pinnacle in four hours. On 12 December 2007, Austrian BASE jumper Felix Baumgartner survived an unauthorized parachute jump from the 91st floor. On 20 November 2005, the First annual Taipei 101 Run Up featured a race up the 2,046 steps from floors 1 to 91. Proceeds were to benefit Taiwan's Olympic teams. The men's race was won by Paul Crake of Australia (10 minutes, 29 seconds), and the women's race by Andrea Mayr of Austria (12 minutes, 38 seconds). On 15 June 2008, Taipei 101 Run Up featured 2,500 participants. The men's race was won by Thomas Dold of Germany (10 minutes, 53 seconds); 2007 champion Marco De Gasperi of Italy finished second and Chen Fu-tsai of Taiwan finished third. The women's race was won by Lee Hsiao-yu of Taiwan (14 minutes, 53 seconds). On 6 December 2014, Japanese idol group HKT48 held a small concert on the 91st-floor observatory as the premiere of their tour in Taiwan.
New Year's Eve fireworks displays
The New Year's Eve Show in Taipei is held at the Taipei City Hall. Visitors have a view of Taipei 101 which is surrounded by fireworks at midnight. Another popular location for crowds to gather to see the fireworks display is the public square of Sun Yat-sen Memorial Hall. For the first three years (2004–2006), the annual fireworks show at Taipei 101 was preceded by the sequential display of numerals in lights on each section on panel displays to count down the last eight seconds to midnight. Since 2007 the building has been completely darkened, then fireworks begin to launch sequentially from the lower to upper sections.
2003–2004: Building still under construction. Spinning lights on the Outdoor Observatory (floor 91) provided a display of sound and lights, but no fireworks were launched.
2004–2005: Grand opening of Taipei 101 celebrated with the first fireworks display. The show lasted 35 seconds. fireworks were launched from section balconies. Festivities included all-day performances by famous entertainers and ceremonial visits by national dignitaries.
2005–2006: Show extended to 128 seconds. Sony sponsored the show, which concluded with a display of the brand name in lights.
2006–2007: Show extended to 188 seconds; 9,000 fireworks were launched. This was Sony's second time sponsoring the event.
2007–2008: Show same length but featuring 12,000 fireworks. Event Sponsor Taiwan Tourism Bureau ended the show with a display, in lights, of a heart over the word 'Taiwan'.
2008–2009: The theme was "Love Taiwan With Your Heart in 2009". The show ended with a heart appearing over the word 'Taiwan' on the light display on the side of the building.
2009–2010: The show to launched 16,000 fireworks and lasted 188 seconds.
2010–2011: Show extended to 288 seconds (100 sec. for flash effects and 188 sec. for fireworks) and included 30,000 fireworks. It was designed by Cai Guo-Qiang, the artist also responsible for Beijing Olympics and World Expo Shanghai's fireworks. The display on the building was accompanied by fireworks going off other buildings in the Xinyi financial district. One concept was for fireworks to spiral up and down the building like dragon crawling.
2011–2012: The show was shortened to 202 seconds. It also gained attention on YouTube, where viewers noticed an apparent "UFO" in the seconds before the fireworks started, later determined to be a radio-controlled glider with lights.
2012–2013: The show was designed by the French pyrotechnics company Groupe F and was 198 seconds in length, featuring 22,000 fireworks launched to an adaptation of Igor Stravinsky's The Firebird. The theme was "Swing for the Future". The words "Time for Taiwan" (both in English and Mandarin Chinese) were displayed in lights at the building to promote Taiwan Tourism Bureau's advertising campaign.
2013–2014: The show lasted 218 seconds and a thematic music was created for the first time by local musicians to commemorate Taipei 101's 10th anniversary.
2014–2015: The show performed for 218 seconds. iSee Taiwan Foundation sponsored the fireworks to promote the beauty of Taiwanese culture and creativity. The firework music was arranged by Mr. Lee, Che-Yi, blended with the famous classical song The four seasons by Vivaldi and many Taiwanese folk music. Performed and recorded by Taipei Symphony Orchestra.
2015–2016: It is the fourth time Groupe F designed the firework show for Taipei 101, with a green theme "Nature is Future" this year. The 238-second display included 30,000 fireworks. It is also the first time to have professional climbers to settle the firework racks onto the building façades. Mr. Lee, Chi-Yi once again arranged the music mixed with international and Taiwanese rhythms reflecting the nature-related theme and Evergreen Symphony Orchestra played the role of performance. A young Taiwanese IT design company BungBungame became the exclusive sponsor supporting a symbolic event showing Taiwan to the world.
2019–2020: Taipei 101 displayed a show with the theme of "Light of Hope, Taiwan", launching 16,000 fireworks at midnight.
Architecture and design
Height
Taipei 101 comprises 101 floors above ground, as well as five basement levels. The first building to break the half-kilometer mark in height, it was the world's tallest building from 31 March 2004 to 10 March 2010. , it is still the world's largest and tallest green building.
Taipei 101 was the world's tallest building, at as measured to its architectural top (spire), exceeding that of the Petronas Towers, which were previously the tallest skyscraper at . The height to the top of the roof, at , and highest occupied floor, at , surpassed the previous records of the Willis Tower: and , respectively. It also surpassed the 85-story, Tuntex Sky Tower in Kaohsiung as the tallest building in Taiwan and the 51-story, Shin Kong Life Tower as the tallest building in Taipei. Taipei 101 claimed the official records for the world's tallest sundial and the world's largest New Year's Eve countdown clock.
Various sources, including the building's owners, give the height of Taipei 101 as , roof height and top floor height as and . This lower figure is derived by measuring from the top of a platform at the base. CTBUH standards, though, include the height of the platform in calculating the overall height, as it represents part of the man-made structure and is above the level of the surrounding pavement. Taipei 101 displaced the Petronas Towers as the tallest building in the world by . The record it claimed for greatest height from ground to pinnacle was surpassed by the Burj Khalifa in Dubai, which is in height. Taipei 101's records for roof height and highest occupied floor briefly passed to the Shanghai World Financial Center in 2008, which in turn yielded these records as well to the Burj.
Overall, Taipei 101 was the tallest building in the world for six years, being surpassed by the Burj Khalifa in 2010. For 12 years it also had the fastest elevator, at 38 miles per hour. It also has the largest wind damper in the world, at 18 feet across. As of 2023, Taipei 101 is the eleventh-tallest building in the world, according to the Council on Tall Buildings and Urban Habitat's official rankings.
Structural design
Taipei 101 is designed to withstand typhoon winds and earthquake tremors that are common in the area in the east of Taiwan. Evergreen Consulting Engineering, the structural engineer, designed Taipei 101 to withstand gale winds of as well as the strongest earthquakes in a 2,500-year cycle.
Taipei 101 was designed to be flexible as well as structurally resistant, because while flexibility prevents structural damage, resistance ensures comfort both for the occupants and for the protection of the glass, curtain walls, and other features. Most designs achieve the necessary strength by enlarging critical structural elements such as bracing. Because of the height of Taipei 101, combined with the surrounding area's geology—the building is located just away from a major fault line—Taipei 101 used high-performance steel construction and 36 columns, including eight "mega-columns" packed with concrete. Outrigger trusses, located at eight-floor intervals, connect the columns in the building's core to those on the exterior.
These features, combined with the solidity of its foundation, made Taipei 101 one of the most stable buildings ever constructed. The foundation is reinforced by 380 piles driven into the ground, extending as far as into the bedrock. Each pile is in diameter and can bear a load of .
Motioneering designed a steel pendulum that serves as a tuned mass damper, at a cost of NT$132 million (US$4 million). Suspended from the 92nd to the 88th floor, the pendulum sways to offset movements in the building caused by strong gusts. The tuned mass damper is visible to all visitors on the 88th through 92nd floors. It can reduce up to 40% of the tower's movements. Its ball, the largest damper ball in the world, consists of 41 circular steel plates of varying diameters, each thick, welded together to form a ball. Two additional tuned mass dampers, each weighing , are installed at the tip of the spire which help prevent damage to the structure due to strong wind loads. On 8 August 2015, strong winds from Typhoon Soudelor swayed the main damper by —the largest movement ever recorded by the damper.
The damper has become such a popular tourist attraction that the city contracted Sanrio to create a mascot: the Damper Baby. Four versions of the Damper Baby ("Rich Gold", "Cool Black", "Smart Silver" and "Lucky Red") were designed and made into figurines and souvenirs sold in various Taipei 101 gift shops. Damper Baby has become a popular local icon, with its own comic book and website.
Structural facade
Taipei 101's characteristic blue-green glass curtain walls are double paned and glazed, offer heat and UV protection sufficient to block external heat by 50 percent, and can sustain impacts of . The facade system of glass and aluminum panels installed into an inclined movement-resisting lattice contributes to overall lateral rigidity by tying back to the mega-columns with one-story high trusses at every eighth floor. This facade system is, therefore, able to withstand up to of seismic lateral displacements without damage. The facade system is also known as a Damper.
The original corners of the facade were tested at RWDI in Ontario, Canada. A simulation of a 100-year storm at RWDI revealed a vortex that formed during a 3-second wind at a height of 10 meters, or equivalent to the lateral tower sway rate causing large crosswind oscillations. A double chamfered step design was found to dramatically reduce this crosswind oscillation, resulting in the final design's "double stairstep" corner facade. Architect C.Y. Lee also used extensive facade elements to represent the symbolic identity he pursued. These facade elements included the green tinted glass for the indigenous slender bamboo look, eight upper outwards inclined tiers of pagoda each with eight floors, a Ruyi and a money box symbol between the two facade sections among others.
Taipei 101's own roof and facade recycled water system meets 20 to 30 percent of the building's water needs. In July 2011, Taipei 101 was certified "the world's tallest green building" under LEED standards.
Symbolism
The height of 101 floors commemorates the renewal of time: the new century that arrived as the tower was built (100+1) and all the new years that follow (1 January = 1-01). It symbolizes lofty ideals by going one better on 100, a traditional number of perfection. The number also evokes the binary numeral system used in digital technology.
The main tower features a series of eight segments of eight floors each. In Chinese-speaking cultures the number eight is associated with abundance, prosperity and good fortune.
The repeated segments simultaneously recall the rhythms of an Asian pagoda (a tower linking earth and sky, also evoked in the Petronas Towers), a stalk of bamboo (an icon of learning and growth), and a stack of ancient Chinese ingots or money boxes (a symbol of abundance). Popular humor sometimes likens the building's shape to a stack of take-out boxes as used in Western-style Chinese food; of course, the stackable shape of such boxes is likewise derived from that of ancient money boxes. The four discs mounted on each face of the building where the pedestal meets the tower represent coins. The emblem placed over entrances shows three gold coins of ancient Chinese design with central holes shaped to imply the Arabic numerals 1-0-1. The structure incorporates many shapes of squares and circles to reach a balance between yin and yang.
Curled ruyi figures appear throughout the structure as a design motif. Though the shape of each ruyi at Taipei 101 is traditional, its rendering in industrial metal is plainly modern. The ruyi is a talisman of ancient origin associated in art with heavenly clouds. It connotes healing, protection and fulfillment. It appears in celebrations of the attainment of new career heights. The sweeping curved roof of the adjoining mall culminates in a colossal ruyi that shades pedestrians. Each ruyi ornament on the exterior of the Taipei 101 tower stands at least tall.
At night the bright yellow gleam from its pinnacle casts Taipei 101 in the role of a candle or torch upholding the ideals of liberty and welcome. From 6 to 10 p.m., the tower's lights display one of seven colors, according to a weekly schedule.
From 26 February to 6 March 2022, the typical colors were replaced by blue and yellow in solidarity with Ukraine, in response to the 2022 Russian invasion of Ukraine.
The adjoining Taipei 101 on the east side connects the landmark further with the symbolism of time. The design of the circular park doubles as the face of a giant sundial. The tower itself casts the shadow to mark afternoon hours for the building's occupants. The park's design is echoed in a clock that stands at its entrance. The clock runs on energy drawn from the building's wind shear.
Taipei 101, like many of its neighboring buildings, exemplifies the influence of feng shui philosophy. An example appears in the form of a large granite fountain at the intersection of Songlian Road and Xinyi Road near the tower's east entrance. A ball at the fountain's top spins toward the tower. As a work of public art the fountain offers a contrast to the tower in texture even as its design echoes the tower's rhythms. The fountain also serves a practical function in feng shui philosophy. A T intersection near the entrance of a building represents a potential drain of positive energy, or ch'i, from the structure and its occupants. Placing flowing water at such spots is thought to help redirect the flow of ch'i.
Interior
Taipei 101 is the first record-setting skyscraper to be constructed in the 21st century. It exhibits a number of technologically advanced features as it provides a center for business and recreation.
The original 2004 fiber-optic and satellite Internet connections permitted transfer speeds up to a gigabit per second.
Two restaurants have opened on the 85th floor: Diamond Tony's, which offers European-style seafood and steak, and Shin Yeh 101 (欣葉), which offers Taiwanese Hokkien cuisine. Occupying all of the 86th floor is Taiwanese restaurant Ding Xian 101. Din Tai Fung, several international dining establishments and retail outlets also operate in the adjoining mall. The multistory retail mall adjoining the tower is home to hundreds of fashionable stores, restaurants, clubs and other attractions. The mall's interior is modern in design even as it makes use of traditional elements. The curled ruyi symbol is a recurring motif inside the mall. Many features of the interior also observe feng shui traditions.
Floor directory
A tenant directory is posted in the first floor's lobby (visible from the Xinyi entrance).
The number 4 is considered an unlucky number in Chinese culture, so instead there is 42A and 43, with no 44th floor.
As of 1 January 2011, the highest occupied office floor (excluding the observatory and restaurants) was 75. The building appears to be at least 70 percent occupied at this point.
The 92nd through 100th floors are officially designated as communication floors, although it is unknown if there are any radio or TV stations currently broadcasting from the top of Taipei 101. The 101st floor indoor/outdoor rooftop observatory opened to the public on 14 June 2019.
The top 92-100 floors are labeled as communications floors.
The 101st floor is home to a private VIP club named Summit 101, according to the observatory brochure. Before 2014, no information about this club was ever made public. In 2014, photos of the exclusive club were shown on TV for the first time. A Taipei Financial Center Corporation spokesman said that only foreign dignitaries, Hollywood film actors, and high spenders in the Taipei 101 Mall (over NT $1 million in purchases) had been invited to the VIP club.
Elevator
The double-deck elevators built by the Japanese Toshiba Elevator and Building Systems Corporation (TELC) set a new record in 2004 with the fastest ascending speeds in the world. At per hour, per second, or 1,010 m/min, the speed of Taipei 101's elevators is 34.7 percent faster than the previous record holders of the Yokohama Landmark Tower elevator, Yokohama, Japan, which reaches speeds of per second (45 km/h, 28 mph). Taipei 101's elevators transport visitors from the fifth floor to the 89th-floor observatory in 37 seconds. Each elevator features an aerodynamic body, full pressurization, state-of-the art emergency braking systems, and the world's first triple-stage anti-overshooting system. The cost for each elevator is NT$80 million (US$2.4 million). In 2016, the title for the fastest elevator was taken away by the Shanghai Tower in Shanghai. Shortly after, the title for the world's fastest elevator was passed on yet again to the Guangzhou CTF Finance Centre. The shuttle double deck elevators only serves 35F/36F and 59F/60F.
Floor plan
Observation deck
Taipei 101 features an indoor observation deck on the 88th and 89th floors, and two outdoor observation decks (91st floor and 101st floor), all offering 360-degree views and attract visitors from around the world. The Indoor Observatory stands above ground, offering a comfortable environment, large windows with UV protection, recorded voice tours in eight languages, and informative displays and special exhibits. Here, one may view the skyscraper's main damper, which is the world's largest and heaviest visible damper, and buy food, drinks and gift items. Two more flights of stairs take visitors up to the Outdoor Observatory. The Outdoor Observatories, at and above ground, is the second-highest observation deck ever provided in a skyscraper and the highest such platform in Taiwan.
The Indoor Observatory is open thirteen hours a day (9:00 am–10:00 pm) throughout the week as well as on special occasions; the Outdoor Observatory is open during the same hours as weather permits. Tickets may be purchased on site in the shopping mall (5th floor) or in advance through the Observatory's website and allow access to the 88th through 91st floors via high-speed elevator.
In 2019, its 101 top floor opened for the first time to the public, starting 14 June with only 36 people given access each day. The 91st-floor observatory used to be the highest floor that open to the public until 14 June 2019 when it was announced by the building's management team that the 101st floor (at 460 m above sea level) will be opened to the general public, with a quota of 36 people per day and is subject to prior booking. Going onto the outdoor viewing platform requires safety equipment, such as a safety belt buckled to the railing.
Other features
Artworks
Many works of art appear in and around Taipei 101. These include: German artist Rebecca Horn's Dialog between Yin and Yang in 2002 (steel, iron), American artist Robert Indiana's 1-0 in 2002 and Love in 2003 (aluminum), French artist Ariel Moscovici's Between Earth and Sky in 2002 (rose de la claret granite), Taiwanese artist Chung Pu's Global Circle In 2002 (black granite, white marble), British artist Jill Watson's City Composition in 2002 (Bronze), and Taiwanese artist Kang Mu Hsiang's Infinite Life in 2013 (aluminum). Moreover, the Indoor Observatory hosts a regular series of exhibitions. The artists represented have included Wu Ching (gold sculpture), Ping-huang Chang (traditional painting) and Po-lin Chi (aerial photography).
Awards
On its opening date, Taipei 101 was awarded the Emporis Skyscraper Award, coming in 1st place.
Taipei 101 was awarded the top award platinum rating, by the Leadership in Energy and Environmental Design (LEED), the globally recognized green building ranking system of the U.S. Green Building Council (USGBC), making the skyscraper the tallest energy conservation building in the world.
In 2017, Taipei 101 was awarded the Asia Responsible Entrepreneurship Award (AREA).
Taipei 101 was awarded the CTBUH Skyscraper Award on the Performance award category.
Gallery
See also
List of tallest buildings in Taipei
List of tallest buildings in Taiwan
Taipei Nan Shan Plaza
List of tourist attractions in Taipei
List of most expensive buildings
References
External links
Taipei 101 Official Website
Website for Vietnamese
Taipei 101 Official Website – Observatory
Taipei 101 Official Website – Mall
YouTube – Taipei 101 New Year Fireworks 2005, 2006, 2007, 2008
National Geographic Channel – Richard Hammond examines Taipei 101
Consulting services by RWDI (wind engineering and emergency ventilation) and Motioneering (tuned mass damper)
Megastructure Supports Taipei's 508-Meter 'Megatower' by Engineering News-Record, a weekly magazine by McGraw-Hill Construction of McGraw-Hill
LEED Official Site
C. Y. Lee Architects Office Official Website
Further reading
2004 establishments in Taiwan
Buildings and structures completed in 2004
Skyscraper office buildings in Taipei
Tourist attractions in Taipei
Shopping malls in Taipei
Shopping malls established in 2004
Expressionist architecture
Former world's tallest buildings
Xinyi Special District
High-tech architecture
Postmodern architecture
Observation towers