Cosa was a Latin colony founded by Rome in 273 B.C. in territory confiscated from the Etruscan city of Vulci. The fortification walls of the ancient town still dominate the coast some ninety miles north of Rome. The town itself became an agricultural and commercial center, whose trade can be traced in part through a distinctive type of amphora to destinations throughout the Mediterranean world.

Cosa's archaeological importance lies in the fact that it provides essential evidence for Roman culture and political organization as they are expressed in structures, and town planning of the republican period, evidence not available in Rome, where republican structures vanished beneath the massive building programs of the imperial age. Cosa IV reports on a group of recently excavated houses between the forum and the Florentine or northwest gate. The volume traces the development of the Roman house, which Frank Brown counts as a major contribution to Roman architecture, from a small urban dwelling of the early colony to the more elaborate houses of the late second and early first centuries B.C., including a Cosan example of the atrium house.

The appearance of Cosa IV, and its companion volume on the forum, Cosa III, adds to the importance of the early colony to the field of ancient studies.