died at Threave soon after. Her monument stands in Lincluden Collegiate Church. A lead seal matrix made for Margaret was recovered during archaeological excavations at Threave. The seal shows her coat of arms, combining the arms of her husband with the Royal Arms of her father Robert III. Although a rare survival, the workmanship is poor suggesting it may have been a trial piece or even a forgery. Downfall of the Black Douglases The power and influence of the Douglases continued to grow. Archibald Douglas, 5th Earl of Douglas, succeeded to his father's estates and in 1437 was appointed Regent to the young King James II. He died unexpectedly in 1439 and in the ensuing power struggle Sir William Crichton, Sir Alexander Livingston of Callendar, and James Douglas, Earl of Avondale (son of Archibald the Grim) conspired to usurp the Black Douglas power. In 1440 they summoned Archibald's children William and David to Edinburgh Castle. 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. James Douglas was the principal benefactor, inheriting the Earldom of Douglas. On James' death in 1443, his oldest son William became 8th Earl of Douglas. 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. The marriage was unpopular with the other nobles who were wary of the power of the Earl, as well as his influence over the young James II who was still a minor. In 1447 Earl William forced the elderly Princess Margaret to give up Threave Castle and retire to Lincluden, finally giving him control of Galloway. He began a series of improvements to the fortifications at Threave, demolishing the earlier outbuildings and constructing elaborate outer defences. These included a defensive wall along the river bank, as well as the "artillery house", a curtain wall with three towers designed to be defended with guns. It is considered to be one of the first purpose-built artillery defences to be built in Britain. In 1452 the Earl seized Patrick Maclellan of Bombie, Sheriff of Galloway, and imprisoned him at Threave. Despite the King requesting his release, Maclellan was murdered. On 22 February 1452,