San Pietro was a cathedral from the 11th century until 1418, the year in which the diocese of Barbaria, including Trexenta, merged with that of Cagliari. The vicissitudes of the church of San Pietro, the patron saint of Suelli, are closely linked to another saint, San Giorgio, a charismatic figure known for his beatitudes and miracles, becoming the first bishop of the Suelli diocese at the tender age of 22. There is some doubt regarding the origins of the building of worship, with the first written mention dating back to shortly after the death of the bishop (1117) and concerning the donations received. Over the centuries, the building was remodelled several times, yet the clear impressions of the 13th-century structure can still be seen, preserved in the façade. The initial significant work in the 13th century was undertaken by Tuscan masters, who transformed the church into a Romanesque-Pisan style.