Siege of Serdica (809)
809 CE.
Shown on the map at 42.667°, 23.330°.
The siege of Serdica (Bulgarian: Обсадата на Сердика) took place in the spring of 809 at modern Sofia, Bulgaria. As a result, the city was annexed to the Bulgarian State and remained so until the fall of the First Bulgarian Empire.
Text from the Wikipedia article Siege of Serdica (809), licensed CC BY-SA 4.0.