Title: Giza pyramid complex
Content:  project. Along with the methods utilized to construct the pyramids, there is also wide speculation regarding the exact number of workers needed for a building project of this magnitude. When Greek historian Herodotus visited Giza in 450 BC, he was told by Egyptian priests that "the Great Pyramid had taken 400,000 men 20 years to build, working in three-month shifts 100,000 men at a time." Evidence from the tombs indicates that a workforce of 10,000 laborers working in three-month shifts took around 30 years to build a pyramid. The Giza pyramid complex is surrounded by a large stone wall, outside which Mark Lehner and his team discovered a town where the pyramid workers were housed. 
Title: Great Pyramid of Giza
Content:  such, many of the speculative errors and confusions about the monument can be traced back to Herodotus and his work. Herodotus writes that the Great Pyramid was built by Khufu (Hellenized as Cheops) who, he erroneously relays, ruled after the Ramesside Period (Dynasties XIX and XX). Khufu was a tyrannical king, Herodotus claims, which may explain the Greek's view that such buildings can only come about through cruel exploitation of the people. Herodotus further states that gangs of 100,000 labourers worked on the building in three-month shifts, taking 20 years to build. In the first ten years a wide causeway 
Title: Great Pyramid of Giza
Content:  tools. In the experiment replicas of these were used to cut a block weighing about 2.5 tonnes (the average block size used for the Great Pyramid). It took 4 workers 4 days (with each working 6 hours a day) to excavate it. The initially slow progress sped up six times when the stone was wetted with water. Based on the data, Burgos extrapolates that about 3,500 quarry-men could have produced the 250 blocks/day needed to complete the Great Pyramid in 27 years. A construction management study conducted in 1999, in association with Mark Lehner and other Egyptologists, had estimated that the total project required an average workforce of about 13,200 people and a peak workforce of roughly 40,000.
Title: Great Pyramid of Giza
Content:  The Great Pyramid of Giza (also known as the Pyramid of Khufu or the Pyramid of Cheops) is the oldest and largest of the pyramids in the Giza pyramid complex bordering present-day Giza in Greater Cairo, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact. Egyptologists conclude that the pyramid was built as a tomb for the Fourth Dynasty Egyptian pharaoh Khufu and estimate that it was built in the 26th century BC during a period of around 27 years. Initially standing at 146.5 m, the Great Pyramid 
Title: History of architecture
Content:  Kingdoms (circa 2600-1800 BC). The most imposing one was the Great Pyramid of Giza, made for Pharaoh Khufu in circa 2589-2566 BC. The Ancient Egyptian pyramids were built with precision, their massive stones so finely joined that the edge of a knife cannot fit between them. The stone blocks were held together by mortar, and the entire structure was covered with highly polished white limestone, with their tops topped in gold. What we see today is actually the core structure of the pyramid. Despite being highly associated with the Ancient Egyptians, pyramids have been built by other civilisations to, like the Mayans or the Aztecs. Due to the lack of resources and a shift in 
Title: Great Pyramid of Giza
Content:  lines of succession, Greaves concluded the year 1266 BC to be the beginning of Khufu's reign. Two centuries later, some of the gaps and uncertainties in Manetho's chronology had been cleared by discoveries such as the King Lists of Turin, Abydos, and Karnak. The names of Khufu found within the Great Pyramid's Relieving Chambers in 1837 helped to make clear that Cheops and Souphis are, in fact, one and the same. Thus the Great Pyramid was recognized to have been built in the 4th dynasty. The dating among Egyptologists still varied by multiple centuries (around 4000–2000 BC), depending on methodology, preconceived religious notions (such as the biblical deluge) and which source they thought was more credible. Estimates significantly narrowed 
Title: Egyptian pyramids
Content:  the great pyramids of Meidum, Dahshur, and Giza. The last pharaoh of the 4th Dynasty, Shepseskaf, did not build a pyramid and beginning in the 5th Dynasty; for various reasons, the massive scale and precision of construction decreased significantly leaving these later pyramids smaller, less well-built, and often hastily constructed. By the end of the 6th Dynasty, pyramid building had largely ended and it was not until the Middle Kingdom that large pyramids were built again, though instead of stone, mudbrick was the main construction material. Long after the end of Egypt's own pyramid-building period, a burst of pyramid-building occurred in what is present-day Sudan, after much 
Title: Egyptian pyramid construction techniques
Content:  of Meidum, the Bent Pyramid, and the Red Pyramid. Also during this period (between 2686 and 2498 BC) the Sadd el-Kafara dam, which used an estimated 100,000 cubic meters of rock and rubble, was built. In October 2018, a team of archaeologists from the Institut Français d'Archéologie Orientale and University of Liverpool had announced the discovery of the remains of a 4,500-year-old ramp contraption at Hatnub, excavated since 2012. This method which aided in lifting the heavy alabaster stones up from their quarries may have been used to build Egypt's Great Pyramid as well. Yannis Gourdon, co-director of the joint mission at 
Title: Egyptian pyramid construction techniques
Content:  and Menkaure's pyramids, the Great Sphinx, the Sphinx, and Valley Temples, 35 boat pits cut out of solid bedrock, and several causeways, as well as paving nearly the entire plateau with large stones. This does not include Khafre's brother Djedefre's northern pyramid, Abu Rawash, which would have also been built during this time frame of 100 years. In the hundred years prior to Giza—beginning with Djoser, who ruled from 2687 to 2667 BC, and amongst dozens of other temples, smaller pyramids, and general construction projects—four other massive pyramids were built: the Step pyramid of Saqqara (believed to be the first Egyptian pyramid), the 
Title: Great Pyramid of Giza
Content:  and slavery. According to Diodorus, the cladding of the pyramid was still in excellent condition at the time, whereas the uppermost part of the pyramid was formed by a platform 6 royal cubit high. About the construction of the pyramid he notes that it was built with the help of ramps since no lifting tools had yet been invented. Nothing was left of the ramps, as they were removed after the pyramids were completed. He estimated the number of workers necessary to erect the Great Pyramid at 360,000 and the construction time at 20 years. Similar to Herodotus, Diodorus also claims that the side of the pyramid is inscribed with writing that "[set] forth [the price of] vegetables and purgatives for the workmen there were paid out over sixteen hundred talents."

Question: how long did it take to build the great pyramid of egypt?
Answer: 20-year period.