Markovo Kale is a fortress located 3.5 kilometres (2.2 mi) northwest of Vranje, Serbia, on a steep rocky crest surrounded by the mountains Krstilovica and Pljackavica. Below the fortress the rivers Devotinska and Mala Reka flow. In historical sources it was mentioned for the first time in 1412, when it was taken by sultan Musa.
The plateau on which the fortress lies is naturally wide on the south side and very narrow on the north side. To additionally secure the east side, the only side from which the fortification was reachable, a long and wide wall was built. The wall followed the edge of the crest, and at the end of the wall was the main tower – built on the highest rock on the northeast end of the crest. On the west side, above the river Devotinska is an unreachable cliff, so no fortifications were necessary on that side.(Wikipedia)