1255

Western Europe

 * August - The final stronghold in southern  falls, eliminating the last refuge of the heretical Cathars after the  engaged in a program to crush the sect, starting in  with the.
 * The death of prompts persecution of s in  on accusations of.
 * becomes the capital of the.
 * The  at, , is completed. It is now a.
 * A survey of royal privileges is conducted, which is included in the, an  seen as a follow up to the  completed in ; the Hundred Rolls is later completed with two larger surveys in / and /.

Central and Eastern Europe

 * May - from  returns to  from his missionary journey to convert the  of central and eastern Asia, his efforts having been unsuccessful.
 * (now Kaliningrad) is founded in.
 * , (in exile in the ), conducts a military campaign to recover  from the ns. He concludes the task successfully a year later in.
 * The is split into
 * The state of  is divided, not to be reunited until.
 * King grants  municipal rights of a royal town.

Asia

 * is dispatched by his brother to destroy the remaining  states in southwestern.

Births

 * , (died )
 * , claimant to the crown of (died )
 * di Buoninsegna,  (died )
 * Grand Prince (approximate date; died )
 * , (approximate date; died )

Deaths

 * -, English prelate and statesman
 * (born )
 * , Archbishop of Sweden
 * , semi-historical hero and founder of the . (approximate date; born c. )
 * , ruler and founder of the.