Siege of Tarnovo
1393 CE.
Shown on the map at 43.083°, 25.650°.
The siege of Tarnovgrad occurred in the spring of 1393 and resulted in a decisive Ottoman victory. With the fall of its capital, the Bulgarian Empire was reduced to a few fortresses along the Danube.
Text from the Wikipedia article Siege of Tarnovo, licensed CC BY-SA 4.0.