Insula (building)
In Roman architecture, an insula (Latin for "island", plural "insulae") was one of two things: either a kind of apartment building, or a city block. This article deals with the former definition, that of a type of building. "Insulae" housed most of the urban citizen population of ancient Rome's massive population ranging from 800,000 to 1 million inhabitants in the early imperial period. Residents of an "Insula" included ordinary people of lower- or middle-class status (the "plebs") and all but the wealthiest from the upper-middle class (the "equites"). The traditional elite and the very wealthy  lived in a "domus", a large single-family residence, but the two kinds of housing were intermingled in the city and not segregated into separate neighborhoods. The ground-level floor of the "insula" was used for "tabernae", shops and businesses, with living spaces above. Like modern apartment buildings, an "insula" might have a name, usually referring to the owner of the building. The owners of these buildings were typically wealthy Romans and even those in the Senate. It was also possible for an "insula" to be owned by several people, such as Cicero, who owned a one-eighth share of  an "insula" and presumably took in one-eighth of its revenue. The inhabitants of the "insula" paid rent to secure their accommodation. Construction. Strabo notes that "insulae", like "domus", had running water and sanitation, but this type of housing was sometimes constructed at minimal expense for speculative purposes, resulting in "insulae" of poor construction. They were built in timber, mud brick, and later Roman concrete, and were prone to fire and collapse, as described by Juvenal, the Roman satirist. Among his many business interests, Marcus Licinius Crassus speculated in real estate and owned numerous "insulae" in the city. When one  collapsed from poor construction, Cicero purportedly stated that he was happy that he could charge higher rents for a new building than the collapsed one. Living quarters were typically smallest in the building's uppermost floors, with the largest and most expensive apartments being located on the bottom floors. The "insulae" could be built up to nine storeys, before Augustus introduced a height limit of about 68 feet. Later, this was reduced further, to about 58 feet. The notably large "Insula Felicles" or "Felicula" was located near the Flaminian Circus in ; the early Christian writer Tertullian condemns the hubris of  multiple-story buildings by comparing the Felicles to the towering homes of the gods. It is posited that a typical "insula" would accommodate over 40 people in only ; however, an entire structure could comprise about six to seven apartments, each covering about 1000 sq ft (92 sq m) in floor area. The only surviving insula in Rome is the five storey Insula dell'Ara Coeli dating from the 2nd century AD, which is found at the foot of the Capitoline Hill. Because of safety issues and extra flights of stairs, the uppermost floors of Insulae were the least desirable, and thus  the cheapest to rent. Other examples outside of Rome are the "insulae" at Ostia. They provide an insight into what an Insula may have been like during the second and third centuries AD. These particular structures at Ostia are also unique in that they show evidence of luxurious "insulae". Due to the rarity of evidence today it is uncertain as to how common these luxury "insulae" were. The floorplan allows us to determine what constitutes one of these luxury "insulae". Firstly, there is a rectangular living space called a "medianum" from which all the other rooms can be accessed. These  attached reception rooms were different sizes at either end and were typically partitioned further into two separated rooms but sometimes remained each as one. Large glazed windows allowed light into these rooms. These windows would often overlook a garden, courtyard or the street. On the adjacent sides of the "medianum" were the "cubiculī", usually two of them. Larger "insulae" at Ostia suggest that the upper floors could have had kitchens, latrines, and even piped water. Further luxurious features seen in Ostia include ornate pilasters or columns decorating exterior doors to staircases leading up to the apartments. The decorations suggest that  these particular Insulae probably housed wealthy individuals who lived there on a long term basis. Simple two to four roomed apartments are also found in Ostia for the lower classes inhabiting an "insula". As seen in the Casa Di Diana, the ground floor contains a narrow corridor with several poorly lit cells that lead to what is believed to be a shared living area. This type of insula can also be found at Capitoline Hill in Rome which may suggest that this particular design could have been a common solution to high housing demand at the time. The latrine and  cistern for drinking water also seem to be shared. This shared accommodation type meant for the lower classes was likely rented both by short term inhabitants and also acted as an inn for short-tenure or itinerant workers. However, this is merely conjecture as there is no direct evidence to support whether they were shared, nor how many inhabited the space at a given time. Regulation and administration. Augustus instituted reforms aimed at increasing the safety of buildings in the city of Rome. Because of the dangers of fire and collapse, the height of the "insulae" were restricted by Augustus  to 70 Roman feet called the "pes" (20.7 m), and again to an unspecified amount by Emperor Nero after The Great Fire of Rome in 64 AD. Emperor Trajan reduced the height to 60 Roman feet (17.75 m). According to the 4th-century Regionary catalogues, there were about 42,000–46,000 "insulae" in the city, as compared to about 1,790 "domūs" in the late 3rd century. Data on the number of "insulae" and to a lesser extent "domūs" are used for classical demography. The city's population in the late 3rd century is thought to have fluctuated between 700,000–800,000, down from more  than 1 million, based also on figures for the amount of grain required to feed the population in Rome and surrounding areas.