The excessive power of the Black Douglas lords led to their overthrow by James II in 1455, after which Threave was besieged and captured by the King's men.

The name Threave is most likely derived from the Cumbric tref, meaning "homestead", suggesting that the island was settled before Gaelic-speaking people arrived in the area in the 7th century.

The chronicler John of Fordun records that, in 1308, Edward Bruce defeated a force of Gallwegians on the River Dee, and afterward "burnt up the island".

[3] Excavations in the 1970s revealed traces of buildings that could be attributed to this period, and which could have formed part of an early stronghold of the Lords of Galloway.

[5] Following the Battle of Neville's Cross in 1346 further risings in Galloway, in support of Edward Balliol, were put down by Sir William Douglas.

[7] Known as "Archibald the Grim", he had been appointed Warden of the West March in 1361, and spent the following years attacking the English on both sides of the border.

[8] The main keep dates from this time, and was one of the first tower houses built in Scotland, standing alone without any outer defensive features.

The excavations in the 1970s revealed remains of additional stone buildings, constructed in the late 14th century, which may represent a hall and a chapel.

[9] In 1384 Archibald attacked and took Lochmaben Castle, the last English stronghold in south-west Scotland, and in 1388 he inherited the title of 3rd Earl of Douglas.

He funded a rebuilding of Sweetheart Abbey near Dumfries, and contracted marriages for his children with the offspring of King Robert III.

His wife Margaret took on the Lordship of Galloway on Archibald's death, and ruled from Threave as Countess of Douglas and Duchess of Touraine for the next 23 years, outliving her son and grandsons.

At the so-called "Black Dinner" that followed, the two boys were summarily beheaded on trumped-up charges, over the protests of the ten-year-old King James II.

The following year he married, with Papal dispensation, his first cousin Margaret, the "Fair Maid of Galloway", daughter of the 5th Earl.

In doing so he reunited the Black Douglas estates with the Lordship of Galloway, still held by the Fair Maid's grandmother Princess Margaret.

[12] He began a series of improvements to the fortifications at Threave, demolishing the earlier outbuildings and constructing elaborate outer defences.

On 22 February 1452, Douglas was summoned to Stirling Castle, under a safe conduct by the King, who requested his aid against the rebellious Earls of Crawford and Ross.

William's brother James Douglas, now 9th Earl, hastily continued the additions to Threave, completing the artillery house as well as earthworks to the north of the keep.

The new artillery house prevented the King's men from taking the castle by force, even when a bombard, a large siege cannon, was brought up from Linlithgow Palace at a cost of over £59.

[15] One myth associated with the siege, which is related by Nigel Tranter, is that the great cannon Mons Meg was built in Kirkcudbright by a smith named Mollance.

James IV visited in 1502, when royal accounts record cloth, wine and falconers being brought to Threave.

[18] In 1542, Robert Maxwell was captured after the Battle of Solway Moss, and forced to hand Threave over to the English invaders.

Around 1800, during the Napoleonic Wars, modifications were made to allow French prisoners to be held there, although it is not recorded that Threave was actually used for this purpose.

[22] Access to the castle is via a boat over the River Dee, from the Threave Estate, which is owned by the National Trust for Scotland and operated as a nature reserve that is home to bats and ospreys.

[29] In the centre of the east wall is a gatehouse, almost 8 metres (26 ft) high, which was formerly equipped with a drawbridge and two inner doors, with a firing platform above.