Geographical position
The town of Cosa stands on the coast of the Tyrrhenian Sea on a rocky headland (114 m above sea level), that in past ages had been connected to the once island of Argentario by the Tombolo di Feniglia (a sandy rise). There were two areas of high ground in the ancient town one to the East and one to the South, divided by a wide depression.
History
The colony of Cosa, Latin by right, was founded by the Romans in 273 BC after the defeat of the allied forces of the Etruscan towns of Volsinii and Vulci (280 BC) and the handover of most of the territory of Vulci, including the coastal stretches. As a result, the new Latin colony of Cosa now controlled a geographic area of about 550 sq. km.
The name derived from the more ancient Cusi or Cusia, a small Etruscan settlement on the site of what is now Orbetello.
The strategic position and its fortress-like characteristics given by the powerful walls surrounding it, are related both to the threat that the Carthaginian navy represented for the Romans around the time that the colonies were founded (the first Punic war started in 264 BC) and to the necessity of having to keep the recently conquered Etruscan territories that had not yet been completely subjugated, under control.
From the beginning, the centre of the town was made up of a dense network of roads that crossed each other at right angles, making long rectangular buildings that were both the houses of the colonised people and larger areas destined for the construction of public buildings. There were two public areas in the town: the acropolis with a religious function and the forum that was the centre of the political life of the community.The colony of Cosa is an example of how colonisation had an influence not only on the town but also on the whole of the territory, with its infrastructures such as bridges, roads, ports and centuriation: it is evident that the controlled territory at Cosa was restructured on the basis of a centralised, coherent plan.

Centuriation was practised also to determine how much farm land to distribute to the sharecroppers:
each was assigned a holding of about 8 or 16jugera (1 or 2 hectares). However the sharecroppers may also have been divided into two or three classes thereby having a right to different amounts of land.
To solve problems of drainage on the coastal plain, a network of canals at right angles to each other was created, where the final stretch of the river Albegna inclines to the sea. The existence today of drainage channels and canals having the same inclination, especially in the Capalbio valley, shows how efficient and valid hydrographic management was in this particularly problematical area.
The town's port was built at the foot of the headland on which the colony stood. Behind the docks, Portus Cosanus was a large coastal lagoon of which only a part remains today i.e. Lake Burano . All the area surrounding the port was equipped with impressive infrastructures that had the purpose of creating a safe refuge under the headland for sea vessels using wharves and breakwaters built with limestone blocks and of preventing the sand from entering the port and the lagoon behind. To this end, in a first phase (the first decades of the II century BC), the Romans exploited the strength of the currents of one of the effluents of the lagoon and a large natural fissure in the rock, today called "Spacco delta Regina" (The Queen's Cleft). These channels were opened or closed, depending on the seasons, by means of wooden bulkheads running along special grooves, so that the forced current swept away the debris that had accumulated in the basin of the port. In a second phase, (the beginning of the I century BC) the "