Siege of Constantinople
813 CE.
Shown on the map at 41.012°, 28.976°.
The siege of Constantinople in 813 (Bulgarian: Обсада на Константинопол) by Khan Krum (Bulgarian: Крум) was a failed attempt to take the city during the Byzantine–Bulgarian wars.
Text from the Wikipedia article Siege of Constantinople (813), licensed CC BY-SA 4.0.