And indeed architecturally, the atrium never lost its significance as the centre of the house; it is to the house as the choir is to a cathedral.[381] And it is easy to see how naturally it could develop into a much more complicated but convenient dwelling; for example, the alae could be extended to form separate chambers or sleeping-rooms, the tablinum could be made into a permanent dining-room, or such rooms could be opened out on either side of it.

A second story could be added, and in the city, where space was valuable, this was usually the case.

The garden could be converted, after the Greek fashion, and under a Greek name, into a _peristylium_, i.e.an open court with a pretty colonnade round it, and if there were space enough, you might add at the rear of this again an _exedra_, or an _oecus_, i.e.open saloons convenient for many purposes.

Thus the house came to be practically divided into two parts, the atrium with its belongings, i.e.the Roman part, and the peristylium with its developments, forming the Greek part; and the house reflects the composite character of Roman life in its later period, just as do Roman literature and Roman art.

The Roman part was retained for reception rooms, and the Lar, the Penates, and Vesta, with their respective seats, retired into the new apartments for privacy.