During the Franco-Prussian War, he served on the French side as a medic.
In 1871 he returned to Paris, and was awarded a doctorate in 1872 for a thesis on the respiratory tract.
After this he travelled extensively in North Africa, Syria, Asia Minor, Spain, Portugal, Switzerland and Italy (visiting also Germany) and then turned to research into the history of the Crusader states and the Byzantine Empire.
In 1903 he was awarded the Medal of the Royal Numismatic Society.He was a friend of Edith Wharton, who described him as looking like 'a descendent of one of the Gauls on the arch of Titus'.
He also corresponded extensively with the Greek writer Penelope Delta, which correspondence influenced several of her historical novels set in Byzantine times.
He was an ultra-conservative, an active supporter of the anti-Dreyfusard movement.
With Edgar Degas, Jean-Louis Forain and Jules Lemaître, he stormed out of the salon of the hostess Genevieve Straus when her friend Joseph Reinach pointed out Dreyfus' innocence.