The Castrelos Bridge is a small medieval bridge located in the parish of Castrelos and used to cross the Lagares River in the Fragoso Valley. It is also known as Balaídos bridge, Lagares bridge or Pereiró bridge.

It is built in granite stone masonry and finished in masonry of the same stone. It is also one of the two old bridges still standing that cross the Lagares river, the other is located in Sárdoma, which gave access to the Pazo de la Caracola, and is still used for pedestrian traffic.

Its origins are uncertain, although it is possible that it has a Roman origin, as this area was highly Romanised, with numerous salting factories, saltworks, villas and a great deal of commercial activity around the Roman-Castre settlement known as Vicus. In addition, some historians have identified various inscriptions on some of the perpiaños.

However, the conformation that can be seen today clearly comes from the Middle Ages, when the bridge underwent many modifications.

In the seventies of the last century the river was channelled due to the advance of the city and the urbanisation of Balaídos, so that the river no longer flows under the bridge. Nowadays the river passes about 10 metres to the north.

In 1987, after the bridge was unprotected and very deteriorated, the Vigo City Council, in collaboration with the Archaeology Department of the Quiñones de León Museum, cleaned and excavated the area, where several stone pieces were recovered and taken to the museum.

After its restoration and protection with a fence, it was declared an Asset of Cultural Interest with the category of historical-artistic monument by resolution of 11 February 1991.