This chapter discusses history of the excavations of Latin colony, Cosa. In the later 1940s Cosa attracted the attention of Frank Brown, the founding excavator at Cosa, of the American Academy in Rome. He saw it as an excavation site that could provide insight into the Etruscan–Roman transition, into the processes of Roman colonization and into the formative phases of Roman Republican architecture. The first stage in the American Academy archaeologist operations involved the clearing and mapping of the site. The most striking feature at the site of Cosa today is the impressive wall circuit formed of massive polygonal blocks of limestone. After the walls, the most impressive remains at Cosa are those of the temple complex on the Arx. After the excavation of the Arx, in 1950 the American Academy turned to the excavation of the forum. The chapter also talks about building of houses, port, hinterland of Cosa.