Sully Island () is a small tidal island of by the hamlet of Swanbridge in the Vale of Glamorgan. It is located off the northern coast of the Bristol Channel, midway between the towns of Penarth and Barry and south of the Welsh capital city of Cardiff. It is part of the parish of Sully, after which it is named, and is registered as a Site of Special Scientific Interest. Sully island is one of 43 (unbridged) tidal islands that can be reached on foot from the mainland of Great Britain. Access to the island is on foot at low tide from the car park of the Captain's Wife public house. A rocky causeway connecting the island to the mainland is uncovered for approximately 3 hours either side of low tide, the island being cut off from the mainland for the rest of the day. All visitors to the island must exercise care and due diligence. There is now a timer near the island which gives visitors tidal times, letting them know if it is safe to cross. During the 13th century, the island was the base for Alfredo de Marisco, a Norman pirate known locally as The Night Hawk. In the Middle Ages the island was well known for its involvement in the local smuggling trade. History Origins There is evidence that the island was frequently visited by both Romans and Vikings and there is archeological evidence for remains of a Saxon multivallate promontory fort occupying the eastern end of the Island, on the summit of which is a Bronze Age barrow. It has been suggested by some that this was an armed stronghold, but it was more likely to have been a defended residence and farm homestead. Port of Swanbridge Swanbridge and the waterfront protected by Sully Island had been used as a commercial harbour and port for several hundred years, although there is no sign of this today. Cargo arrived and departed via the St Mary's Well Bay Road, which is now blocked off to through traffic, en route for the traditional market at Canton Cross in Cardiff. As late as the early 1970s the harbour's iron mooring rings could still be seen at the eastern end of the bay. During the 16th century several historical records show that the trader masters were supposed to pay an import duty to local officials, but many attempted to avoid