The Cotton Library fire that damaged the Beowulf manuscript occurred in 1731. The blaze began at Ashburnham House in Westminster on 23 October, when the building housed Sir Robert Cotton's collection of medieval manuscripts.
The manuscript survived, but its edges were scorched and weakened. Later handling and rebinding caused additional letters and words to crumble or become hidden, leaving some passages difficult to reconstruct. Beowulf survives in only one medieval manuscript, now usually called the Nowell Codex or Cotton MS Vitellius A XV.
The fire was disastrous for the Cotton collection: many manuscripts were destroyed outright, while others were damaged. The surviving books eventually became part of the foundation collections of the British Library. A common mix-up is to confuse the fire date with later stages of Beowulf scholarship: the manuscript was first transcribed in 1786, decades after the fire, and early editors sometimes had to rely on older descriptions or copies to recover damaged readings.