Along the road leading to Tharros there is the church of San Giovanni di Sinis, which probably dates back to the 5th century, and is therefore one of the most ancient churches in Sardinia still in use. The first structure had a central plan with a dome; in the 11th century it was enlarged with early Romanesque forms, and the interior was divided into a nave and two aisles separated by low arcs and heavy pillars; the two aisles were covered with barrel vaults, while the nave and the apse were covered with the dome. The church still preserves the original central dome supported by four solid arcades.