Have you ever been inside a roman apartment house? The building of the Ara Coeli, of which there are four floors left and the remains of other two, is the only example of a condominium of the imperial time preserved in Rome. The term insula referred to the houses to let, that the need for housing for the growing population and a shortage of building land induced to develop in height The building, of the IInd century AD, is in brickwork but the bottom wall rests directly on the rock and is built in opus reticulatum dated to the Ist century A.D. The entire facade of the Insula is not visible, the ground floor is in fact about 9 meters below the current street level. The façade opened on a courtyard with a portico and five tabernae running some unknown business. Above the entrances to the tabernae are the windows of the mezzanines, with a mosaic floor, where probably lived the owners of the stores below. It is estimated that about 380 people lived in the building.