Torre di Chia, Coastal defense tower in Chia, Italy.

Torre di Chia is a cylindrical limestone watchtower about 13 m high and over 10 m in diameter, with walls roughly 2.5 m thick, standing unroofed on the hilltop that was the acropolis of ancient Bithia. Its entrance, reached by a stair on the west side, is 5 m above ground and leads to a vaulted first floor supported by a central column, from which a stone spiral staircase climbs to the gun platform.

Spanish authorities built this watchtower in the late 1500s as part of a defense network against pirate raids along the coast. This system of towers developed because the shore faced regular threats from sea-based attacks.

The tower's original name, I Santi de Quaranta de Quia, was used from 1594. It was manned by a commander, a gunner and three soldiers, with two more posted outside. Three cannons, 6- and 8-pounders, stood on the gun platform.

The tower stands on the promontory between the beaches of Su Portu and Sa Colonia, above the Chia settlement with its hotels and campsite. The entrance is on the west side, reached by a stair about 5 m above the ground; inside, a vaulted first floor on a central column leads by stone spiral stair to the gun platform. The interior and platform can be visited for a fee.

Nearby lie archaeological remains of Bithia, a former Phoenician and Punic settlement with artifacts spanning many centuries of maritime activity. These discoveries reveal the location held importance long before the Spanish watchtower was built.