For five hundred years Carlisle Castle had been England's principal stronghold on the Scottish border. When civil war broke out in 1642, the castle's geographic remoteness was a kind of armor in itself: Parliamentarian forces were busy further south, so Carlisle's Royalist garrison was simply ignored for two years. That ended on 2 July 1644, when Cromwell's New Model Army and the Scottish Covenanters destroyed the main Royalist northern army at Marston Moor near York. The Royalists lost 5,500 men, all their gunpowder, and the will of their commander, the Marquis of Newcastle, who fled the country in embarrassment. Two weeks later York surrendered. The Royalist cause in northern England had ceased to exist except as scattered garrisons in places like Carlisle. Alexander Leslie, commanding the Covenanter army, methodically began collecting them.

Leslie reached Carlisle in late October 1644 with 4,000 Covenanters. He did not attack. He set up four small siege works on the four major roads into the city, garrisoned by cavalry: one in the churchyard at Stanwix on the north road with three small cannon, the others little more than fortified positions for sixty to a hundred horsemen each. The encirclement was deliberately loose. There was still room outside the walls for cattle to graze, which is exactly what the Royalists exploited. For six months the only fighting at Carlisle was small skirmishes when Royalist parties rode out to round up cattle. Leslie watched and waited. He had seen this war's pattern; he did not need to spend lives on stone walls when time would do it for him.

In the spring of 1645 English Parliamentarian forces joined the besiegers, and Leslie finally began to close his fist. He moved his siege works inward, dug new fortifications, and made it harder and harder for the Royalists to slip out for food. The successful sallies dwindled. Food inside the city dwindled with them. The garrison ate the horses first, the natural casualties of any starving army. Then dogs. Then rats. The contemporary chronicler does not record how the people of Carlisle, trapped inside with the soldiers, fared, but it cannot have been better. In June 1645 King Charles lost the Battle of Naseby and with it any realistic hope of relief. On 25 June, out of food and out of hope, Sir Thomas Glemham surrendered the city and castle.

Leslie's terms were unusually generous. The garrison would march out as free men, colours flying, drums beating, with their firearms and twelve charges of powder each, free to walk all the way back to their king. The people of Carlisle would not be harmed. Their homes would not be looted. Whatever Leslie's reasons, whether mercy, exhaustion, or simple pragmatism about the war's eventual outcome, the contrast with the Carlisle siege of a hundred years later was striking. In 1745 the Duke of Cumberland would offer no such terms, and Carlisle's Royal Border Regiment would still be quartered in the same castle three centuries later. The walls Leslie spared are the walls visitors walk today.