San Teodoro rises on the ruins of the city of Coclearia, built by the Romans among the hills of Citai, Lu Casteddu, the sea and the street of Karalibus-Oliam per oram.
The city of Coclearia, which once had its port in the present locality of Lu Niulioni, had a certain importance during the imperial period, as witnessed by many findings like plates, coins, amphoras and jewels. In 235 a. D., pope Ponziano and the priest Ippolito, which at that time had been banished to the isle of Molara, brought the inhabitants of Coclearia in contact with Christianity. In 455, after the fall of the Roman Empire the Vandals invade Sardinia and dominate the island until the Byzanthine general Belisario defeats them and Sardinia goes to the Eastern Roman Empire.
In 1479, after the Aragonese conquest and after the marriage of Ferdinand the Catholic and Isabella of Castile, the two kingdoms of the peninsula consolidate, Spain is born, Sardinia becomes Spanish and the dismembered Gallura is given to the feudataries.
In 1720, after the treatise of London of the Year 1718, Sardinia goes to the Savoys.