Definitely abandoned the city of Tharros, starting from 1070, Oristano became the new capital of the Giudicato of Arborea (10th century - 1410). The inhabitants of Tharros, in fact, tired of the continuous threats and incursions of the Saracen pirates, decided to move further inland and thus came to Oristano, an inhabited center that already existed in the Byzantine era. Immediately the new capital had a defense system that was strengthened at the end of 1200 by King Mariano II. This is the reconstruction of the city of Oristano at the end of the fourteenth century, equipped with three major towers located near the main entrances of the city and 28 minor turrets to strengthen the walls. To the north the tower of Mariano II, also known as Porta Manna or Porta Pontis, to the south the tower of San Filippo, identical to the first, connected to the palace of residence of the king and his court, to the east the tower of Portixedda, a small tower that it was born like the previous ones with a square base but which now has a circular base and a truncated conical shape, the result of a remake that took place in the Spanish era. A moat fed by the waters of the nearby Tirso river ran along the walls making this city even more conquerable which, rebuilt here, displays the most important religious buildings of the period: the Romanesque Cathedral of Santa Maria Assunta and its octagonal bell tower without the "Cipollone" in polychrome ceramic added in the eighteenth century, the convent and church of San Francesco, the Giudicale hospital, the church of San Mauro, the square-plan church of the Byzantine period dedicated to San Saturnino and finally the church and convent of cloistered nuns of Santa Chiara.

The model reconstructs the city of Tharros at the time of Emperor Constantine (beginning of the 4th century AD). The city, of Phoenician foundation, is brought to light with the temples of Jupiter, Juno and Minerva, the baths, the aqueduct with two orders of arches, the amphitheater and the road system. The city of Tharros is located in a system of valleys dominated by the low reliefs of the Torre di San Giovanni and Su Murru Mannu, which shelter it from the dominant north-west wind. In an urbanized area perhaps already in the Phoenician age, but certainly in the Carthaginian period, the city was inhabited until the beginning of the second millennium after Christ. The viability was affected by the geomorphology of the site, adapting to the contour lines, with the exception of the northern sector where at an indefinite moment, perhaps already in the Punic age, two almost straight and parallel roads were traced that connected the lower city with that high. The urban planning of Tharros did not vary sharply with the advent of Roman domination at the end of the third century BC. Evident urban redevelopment measures can only be seen in the height of the imperial age, with the rearrangement of the strip overlooking the Gulf of Oristano, where two thermal buildings were built. around the middle and end of the 2nd century AD, while a third spa complex was built in an area behind the thermal baths N.1 in the 2nd-3rd century AD A small aqueduct that brought water to the city by capturing it from a well fresh water located half a kilometer north of Tharros was built around 200 BC. An arena for gladiator games and venationes was still built in the advanced imperial age on the top of the Su Murru Mannu hill. The port, in Roman times, seems to be located in the Gulf of Oristano not far from the area of the northernmost spa complex.