Insula ("island"): Latin name for a housing block in a city built according to the Hippodamian Plan.
The Hippodamian Plan is, essentially, a city plan that looks like a gridiron, named after Hippodamus of Miletus, who designed the new port of Athens, Piraeus, in the mid-fifth century BCE. The Romans used this design as well, using it when they expanded existing cities (e.g., Pompeii) and founded new cities (e.g, Augusta Emerita). They called the housing blocks insulae, "islands". A typical insula was square or rectangular. The central market could occupy one or two insulae.