Portencross Castle, also known historically as Portincross Castle, is situated on the west coast of Scotland, about 3km from West Kilbride. The site has been fortified since the 13th Century. The present building is thought to date to the 14th Century and later when the castle was moved from the nearby hill to its present site overlooking the harbour.
In the castle's earliest days, it was known as "Arneil" (alternatively spelled "Arnele" or "Ardneil"), and it stood atop Auld Hill. Portencross is believed by some to have been a royal residence, as it is known that several charters of the first two Stuart kings were signed at the castle.
The castle is also believed to be the last mainland resting place for many former Scottish kings. Between the times of Cináed mac Ailpín (810-858) through to the reign of Máel Coluim mac Donnchada (1030/38-1093), the bodies of former kings were taken by road from the east of Scotland, and from Portencross they were ferried to Iona where they would be buried.
The castle was rebuilt in the 14th century, not on Auld Hill, but instead on a rock promontory at the bottom of the hill, overlooking the Firth of Clyde. From this location, Robert II signed several more Royal Charters, and the castle remained occupied until the roof was blown off during a violent storm in 1739. The castle walls still remain in place today, but the building is badly in need of repair and in hazardous condition.