With its five towers arranged around the central keep, Arrubiu is the only certainly known pentalobate nuraghe in Sardinia. Added to the original central tower, the five towers progressively strengthened the defences of the complex and the spaces used by the community. The site thus became a fortified citadel.
The five-towered bastion is surrounded by the outwork, a second fortified wall with seven towers and wide inner courtyards. From the central courtyard you reach the main tower (A) and the five peripheral towers (C, D, E, F, G), which preserve typical features of Nuragic architecture: wall niches, service rooms and internal stairways. The central tower houses a room covered by a tholos, a false dome built with rows of stones projecting ever closer towards the top.