 Then, in 1223, Archbishop Henry de Loundres attached the deanery of Tallaght to St. Patrick’s Cathedral in Dublin.Gradually, the town of Tallaght grew up around the monastery, and the English-appointed archbishop of Dublin, built (or possibly restored) a palace there.In 1324, the palace was fortified to protect the English in Tallaght from the marauding O’Byrne clan, exposing a need for protection and triggering the building of an Anglo-Norman castle, Belgard, just to the east of the monastery site.