Where Am I?

CLUES

1. The ruins of this ancient city include obelisks, stone pillars, royal tombs and castles.
2. The kingdom, at the crossroads of Africa, Arabia and the Greco-Roman world, once was the most powerful state between Persia and the Eastern Roman Empire.
3. Emperors continued to be crowned in the city long after its political decline in the 10th century.
4. A church in the region is said to hold the biblical Ark of the Covenant.

ANSWER  The ancient city of Aksum, northern Ethiopia