The cemetery for Peterborough Cathedral is to the north of the building. Thousands of people were buried there, from monks to grave diggers. In the past, any people who had their funeral in the cathedral exited the building via the north door, which gave direct access to the graveyard. This is the last door that their body would pass through, so it is known as dead man's door.
In 1548/9 the lock of the door needed repairing, which is not surprising given how old the door is. Two pence was paid for 'mending the loke [lock] of the dedmans dore [door]',(1) which appears a bargain in modern terms. No records exist to say if the lock was needed to keep the living or the dead out of the cathedral!
(1) W. T. Mellows, The Last Days of Peterborough Monastery, Northamptonshire Record Society, 1950, p107