Epilogue, p.666, f.1
"The Caliphate began with the election of Abu-Bakr in A.D. 632 and lasted
until A.D. 1258, when Hulagu Khan sacked Baghdad and put
Mu'tasim-Bi'llah to death. For nearly three centuries after this
catastrophe the title of Caliph was perpetuated in Egypt by descendants of
the House of Abbas who lived under the protection of its Mameluke rulers,
until in A.D. 1517 Sultan Salim, the Osmanli, having conquered the
Mameluke dynasty induced the helpless Caliph to transfer to him the title
and insignia." (P. M. Sykes' "A History of Persia," vol. 2, p. 25.)