[2][3] Most of Runciman's historical works deal with Byzantium and her medieval neighbours between Sicily and Syria; one exception is The White Rajahs, published in 1960, which tells the story of Sarawak, an independent state founded on the northern coast of Borneo in 1841 by James Brooke, and ruled by the Brooke family for more than a century.

"[8] According to Christopher Tyerman, Professor of the History of the Crusades at Hertford College, Oxford,[9] Runciman created a work that "across the Anglophone world continues as a base reference for popular attitudes, evident in print, film, television and on the internet.

"[10] In his personal life, Runciman was an old-fashioned English eccentric[further explanation needed], known as an æsthete, raconteur and enthusiast of the occult.

According to Andrew Robinson, a history teacher at Eton, "he played piano duets with the last Emperor of China, told tarot cards for King Fuad of Egypt, narrowly missed being blown up by the Germans in the Pera Palace Hotel in Istanbul and twice hit the jackpot on slot machines in Las Vegas".

[13] There is little evidence of a long-term lover, but Runciman boasted of a number of casual sexual encounters, and told a friend in later life: "I have the temperament of a harlot, and so am free of emotional complications."

[4][16] Edward Peters (2011) says Runciman's three-volume narrative history of the Crusades "instantly became the most widely known and respected single-author survey of the subject in English.

"[17] John M. Riddle (2008) says that for the greater part of the twentieth century Runciman was the "greatest historian of the Crusades."

He reports that, "Prior to Runciman, in the early part of the century, historians related the Crusades as an idealistic attempt of Christendom to push Islam back."

Throughout his history Runciman portrayed the crusaders as simpletons or barbarians seeking salvation through the destruction of the sophisticated cultures of the east.

[19]Mark K. Vaughn (2007) says "Runciman's three-volume History of the Crusades remains the primary standard of comparison."

"[20] Tyerman himself has said, "It would be folly and hubris to pretend to compete, to match, as it were, my clunking computer keyboard with his [Runciman's] pen, at once a rapier and a paintbrush; to pit one volume, however substantial, with the breadth, scope and elegance of his three.