The first news of Cosededa parish date from the end of the 9th century and beginning of the 10th century, when Bishop Sisnando of Iria mentioned it in a document. Later on, in the 12th century, it appears on several occasions (1124, 1164) as a monastery for nuns.
What remains from the Romanesque building of that same century is the entire sanctuary, being one of the biggest and most beautiful in the province of Pontevedra. It has a pentagonal shape, with each section divided by attached semi-columns, and is joined to the nave by means of a rectangular section housing the triumphal arch leading to the apse. It is decorated with geometric and chequered motifs, small roses and intertwined circles, which are frequently found in Romanesque symbols.