There are records that there was a church at this location of current St Mary's Church before the Norman conquest of Wales as it is mentioned in Domesday Book and by a charter from King John of England. However, there is nothing surviving in the current church building from that period. This is reportedly because of Augustinian canons from Llanthony Secunda visited and built the church on top of the older church that was dedicated to St Bride dating from around AD 900 at the behest of Walter of Gloucester after the construction of Caldicot Castle. The earliest part of the church is the base of the tower, which comes from the 14th century, along with the nave and chancel, which was part of an enlargement programme at the time. The tower was not fully completed until the 16th century.
In the 1850s, the 15th-century north aisle was rebuilt by Henry Woodyer, as well as most of the stained glass windows being replaced. In 1905, the chancel was refitted and many of the Victorian additions were changed.
References:The Cathedral of Saint Mary Major, often called Lisbon Cathedral or simply the Sé, is a Roman Catholic cathedral located in Lisbon, Portugal. The oldest church in the city, it is the seat of the Patriarchate of Lisbon. The cathedral has survived many earthquakes and has been modified, renovated and restored several times. It is nowadays a mix of different architectural styles.
The site where it stands was the principal mosque of Lisbon when it was an Arab settlement. The construction of the cathedral started around 1150, three years after the city was conquered from the Moors during the Second Crusade. Shortly after the victory the English knight Gilbert of Hastings was named bishop of the city of Lisbon.
One good reason to visit the Cathedral is to visit its charming cloisters located in the back. There are several tombs in the cathedral, the most notable of which is the beautifully sculpted tomb of Lopo Fernandes Pacheco and his wife.