Cowal before it was the defended medieval homestead of the MacEwens; at first there was a palisaded enclosure, and then a promontory fort with a timber rampart. The remote areas in the north east of Cowal, which were theoretically under the dominion of Clan Lamont, were used by Scottish kings for hunting; indeed, Cowal was the last part of Britain to have wild boar. When King John Balliol was threatened by his rival, Robert de Bruys, Balliol's ally, the king of England, established Henry Percy at Carrick Castle, in the region; likewise Dunoon Castle further south. De Bruys expelled the English
Cowal in the 19th century, the traditional provinces were formally abolished, in favour of counties aligned with sheriffdoms, so Cowal became merely a part of the county of Argyll. The history of the Cowal is tied into the clans who inhabited it. Seemingly, in the 11th century, an unidentified heiress of the Cenel Comgaill married Anrothan, grandson of the king of the Cenél nEógain, from Ulster. Clan traditions argue that Anrothan's lands were passed down to a descendant named Aodha Alainn O'Neil, who had the following sons: Excavations carried out at Castle MacEwen showed the site had several stages of development