A thousand years of Roman warfare in the east: the sieges of Constantinople, the reconquests, the defeats, and the emperors who fought them.
The eastern Roman empire outlived the western by almost a thousand years, and spent most of them fighting. The archive covers that span from Justinian's reconquest of Africa and Italy in the 530s to the fall of Constantinople in 1453 — the longest continuous military history of any polity it holds.
The shape of it is not a straight decline, which is the single most common misreading. The empire lost Syria, Palestine and Egypt to the Arab conquests within a decade of winning a twenty-six-year war against Persia, and then held its remaining territory against two enormous sieges of its capital. It recovered in the tenth century under Nikephoros Phokas and Basil II to become the strongest state in the Mediterranean, lost Anatolia after Manzikert less through the battle than through the civil wars that followed it, recovered again under the Komnenoi, and was destroyed not by an enemy but by a crusade it had helped to provoke.
Constantinople is the thread. The city was besieged by Avars, Persians, Arabs, Bulgars, Rus and Vikings across nine centuries without falling, and when it did fall in 1204 it fell to allies. The empire restored in 1261 never recovered from that, and the last two centuries are a long defensive contraction against the Ottomans.
This is the archive's deepest single subject, built out across fourteen milestones of dedicated research.