Portsmouth Cathedral is a 12th century church that became elevated to cathedral status in the 20th century. The core of the building was completed in only 16 years, to a cruciform plan with a crossing tower. The style is transitional Gothic.
In 1180 Jean de Gisors granted land to the Augustinian canons of Southwick Priory to build a chapel dedicated to Thomas Becket, whose murder by 4 knights in Canterbury Cathedral just a decade before must have been fresh in Gisors mind. The chapel served as a chantry, with priests to say mass for Gisors and his family, and became in time a parish church, expanded over time as the new town of Portsmouth grew in importance.
The church was built to a cruciform plan, with a central tower rising over the crossing. Aside from its ecclesiastical function as a bell tower, the chapel tower also served a practical purpose as a lighthouse and a lookout point for ships in the channel. In 1449 a group of local sailors murdered the Bishop of Chichester. In retribution, the entire population of Portsmouth was excommunicated by the Pope so the church was forced to close. Thankfully, the closure was not permanent, and Elizabeth I worshipped in St Thomas during a visit in 1591. During the Civil War, the Royalist garrison of Portsmouth used the church tower as a lookout point to watch troop movements of Parliamentary soldiers besieging the town. Parliamentary gunners fired on this makeshift lookout post and caused huge damage to the nave and tower, though surprisingly no one in surrounding buildings was harmed. When Charles II took the throne in 1660 he called upon churches across the country to contribute the £9000 needed to restore St Thomas. The medieval nave and tower were rebuilt from 1683, replacing the medieval furnishings with neoclassical decoration. A mark of the growing congregation are the galleries, added in 1708 and enlarged in 1750.
In May 1927 the parish church of St Thomas of Canterbury became the cathedral of the new diocese of Portsmouth and its mother church and the base for the Bishop of Portsmouth.