The Great Siege of Scarborough Castle was a major conflict for control of one of England's most important stone fortresses during the English Civil War (1642–1651), fought between the Roundheads or Parliamentarians, and the Royalists loyal to King Charles I (reigned 1625–1649). In February 1645, Parliamentarians laid siege to the castle. For five months, they bombarded it, destroying most of the keep, and engaged in bloody fighting before the defenders finally surrendered.
This was a significant though not permanent victory. There was a second, far less bloody and destructive, siege later in 1648 when the new garrison switched sides. The castle finally came under Parliamentarian control in 1649, and remained so until the Restoration (1660). (The castle actually changed hands seven times between 1642 and 1648.)
Early in the English Civil War, Scarborough, its castle and strategic supply port were first held (in September 1642) for Parliament by Sir Hugh Cholmley. In March 1643, he was persuaded to change sides. Cholmley actually lost the castle in a bloodless takeover by his own cousin, Captain Browne Bushell, in the same month while away at York, but persuaded him to give it back. Cholmley ordered the castle to be refortified, including the establishment of the South Steel Battery for artillery.
After March 1643, although Cholmley was the only Royalist commander at work in east and north Yorkshire, his forces felt so secure at Scarborough that they could move almost freely throughout the region, targeting Parliamentarian positions. In May, Cholmley's cavalry moved north of Whitby, 20 miles away, and pillaged the estate of the Earl of Mulgrave, a loyal Parliamentarian. In June, Cholmley captured the marketplace at Beverley, some 30 miles from the castle, and from September to October 1643 he was present at the unsuccessful second Siege of Hull.