J. B. Bury's History of the Later Roman Empire

Such a joy to leave current events for 900 pages of crystal-clear, highly readable prose about the early Byzantines/late Romans. 

Bury was Irish, and some kind of Celto-Druidic sorcery has to be afoot when fifty pages of close description of Byzantine military, administrative, and ecclesiastical bureaucracy is as riveting as a racy novel.

Check it out sometime!