In the 100s AD, big cities in Rome had apartment buildings called insulae, or islands because they took up entire city blocks. They were normally three to four stories tall and made of wood. Later they switched to brick, because of the tendency of fires to ruin the insulae. There were almost 50,000 insulae in the 100s AD and less than 2,000 private houses.
There are many insulae still preserved to this day. There are especially lots of insulae in the Roman port city of Ostia, near Rome. Insulae can be seen in Pompeii and in Italica, Spain. Most of the urban population lived in the insulae.
The ground level of the insulae was used for shops and businesses. Interestingly, the private houses and insulae weren’t segregated, but intermingled throughout the city. The insulae tended to have names and they often referred to the owner of the individual insulae.