6 August – Expedition by Henry III to Gascony to repel a rumoured invasion from Castile. Eleanor of Provence is regent and de facto Lord Chancellor in England during her husband's absence.
Following the death of "Little Saint Hugh of Lincoln", in an instance of blood libel, nineteen Jews of Lincoln are executed by royal command on suspicion of being involved in the boy's murder.[7]
A survey of royal privileges in England is conducted, which is included in the Hundred Rolls.[8]
August – A gold penny is introduced, but swiftly withdrawn when its bullion value proves greater than its twenty pence face value.[7]
c. September – 1257 Samalas eruption: Mount Samalas volcano erupts on Lombok Island in Indonesia; the resultant climatic changes combine with a second successive poor grain harvest this summer in Britain to produce famine, killing an estimated 17,000 in Britain (15,000 in London).[10][11]
Brothers of Penitence (Fratres Saccati, 'Brothers of the Sack') first settle in England, in London.[12]