In a beautiful setting with excellent views of the Mourne Mountains and Carlingford Lough, Greencastle is mainly 13th-century in date. It was built at royal expense and guarded the southern approach to the Anglo-Norman Earldom of Ulster.
After capturing the town of Carrickfergus in 1315/16, a Scottish army under Edward Bruce headed to the important town of Dundalk, one of the seats of Anglo-Norman power in Ireland. It was also a source of much-needed supplies. The Scottish force marched south, wreaking havoc on the Anglo-Norman Earldom of Ulster. It is likely that the settlements at Dundonald, Downpatrick and Dundrum were razed at this time, with Greencastle captured by the Scottish army of Edward Bruce and a garrison was placed in it under the command of Robert de Coulrath.
It was afterwards retaken by the Anglo-Normans.
Even after the ignominious end to the campaign in 1318, Edward’s brother Robert Bruce continued to maintain an interest in Ireland, even visiting the island on at least two occasions near the end of his life. It is known that in 1327 he visited Glendun on the east coast of County Antrim, and landed at Larne the following year. In 1328 he proposed holding a meeting at Greencastle in County Down to agree a peace treaty between the English and the Scots.
The castle continued to be used until the 1600s. It is now in state care. The most substantial part of the castle to survive is the rectangular keep. Only portions of the surrounding curtain wall remain. The ditch around the curtain wall was cut from rock.
References:Carlsten is a stone fortress built on the orders of King Carl X of Sweden following the Treaty of Roskilde, 1658 to protect the newly acquired province of Bohuslän from hostile attacks. The site of Marstrand was chosen because of its location and its access to an ice free port. Initially a square stone tower was constructed, but by 1680 it was reconstructed and replaced by a round shaped tower. Successive additions to the fortress were carried out, by the inmates sentenced to hard labour, until 1860 when it was reported finished. The fortress was decommissioned as a permanent defense installation in 1882, but remained in military use until the early 1990s.
The fortress was attacked and sieged twice falling into enemy hands. In 1677 it was conquered by Ulrik Frederick Gyldenløve, the Danish military commander in Norway and in 1719 by the Norwegian Vice-Admiral Tordenskjold. At both occasions the fortress was returned to Swedish control through negotiations and treaties.