[Fiji Hill]

Archaeologists recently investigated accumulated refuse in trash mounds at a Byzantine settlement called Elusa in Israel's Negev Desert... trash disposal -- once a well-organized and reliable service in outpost cities like Elusa -- ceased around the middle of the sixth century, about 100 years prior to the empire's collapse.

The Roman Empire lost a lot of territory to the Arabs in the seventh century, but it didn't collapse. In fact, it made a comeback late in the first millennium AD. The final decline began, arguably, with the Battle of Manzikert in AD 1071.

[Cronos]

The loss of Egypt and North Africa were hard - those were the bread basket areas (incredible as it may seem today)

Manzikert was hard yes, but terminality was caused by the IV Crusade diverting to attack and conquer Constantinople in 1204 (note: i'm Catholic but I still see this as a mistake, up there with the Crimean war)