Porto Cathedral is the most important religious edifice in the city of Porto. It has been declared a national monument. It is located near the walls that once protected the city, and its building somewhat resembles a castle with arches from the outside. The construction of the cathedral began during the 12th century, but It was rebuilt and renovated several times over the centuries, which explains why the cathedral is a mixture of different architectural styles such as Baroque, Romanesque and Gothic.