An insula was a type of lower class housing for the poor. The insula was hastily constructed and made of cheap construction materials. This meant that the insula could collapse at any time and kill the residents without much effort. The insula were overpopulated and prone to the spreading of disease. Space was limited in Rome so buildings were built as high as possible to accommodate as much people as possible. In fact, some of the remains of the top floors of the insula near the Capitolium are still intact.

Speaking of floors, the bottom floors were usually reserved for poultry and dairy shops. The upper floors were living quarters where families lived in poorly ventilated rooms. The poor ventilation made it easy for fires to spread to other floors. Since the insula was not equipped to handle mass exits for emergency purposes, some people died while trying to run from major fires. Basically the insula was the modern version of slum apartments for the poor.

One of the better preserved insula is in the town of Ostia. There is evidence that there were staircases in the insula, but there is no evidence that any system of pipes were installed in the insula. This meant that residents had to use public latrines and carry water from nearby resources. The insula is an eye opening study into how the poor in a wealthy and powerful nation lived.