During his reign from 527-565, the Byzantine Emperor Justinian consolidated this site, originally built by the Palmyrene Queen Zenobia, to protect his Empire against Persian encroachment from across the Euphrates River.  The robust gypsum walls of this fortress city form a triangle:  the base touching the banks of the Euphrates, with the two sides culminating in a citadel.  Isolated from other settlements, the city escaped the plundering of its magnificent masonry over the centuries, and thus remains one of the best preserved and most interesting Byzantine sites in Syria.