The Romanesque church of San Nicola di Trullas, located in Semestene, is a fascinating example of Sardinian medieval architecture, whose history is intrinsically linked to its name. The etymology of the place name 'Trullas' offers interesting insights into the origins of the building. It is hypothesised that it derives from the ancient name of a Byzantine domed church, with the term 'trudda' - the Logudorese version of the Greek and Latin 'troulla', meaning 'dome' - suggesting possible Byzantine-Oriental architectural influences in its original conception. The church's documented history begins in 1113, when the Athen family ceded it to the Camaldolese monks. This transfer of ownership not only marks a crucial moment in the building's history, but also provides valuable information on the religious and feudal dynamics of medieval Sardinia, highlighting the significant role of the monastic orders in the diffusion of architectural and cultural models on the island. From an architectural point of view, San Nicola di Trullas is distinguished by its single-nave structure, covered by cross arches. This solution, in addition to creating a unified and harmonious interior space, represents a significant technical evolution in Romanesque architecture, allowing for a better distribution of weight and greater illumination of the interior.