There are legends behind the name I found 3 different :
1. There footmark of the devil in on of the stones?
2. During Turks occupation, local Turk wants a Bulgarian woman for a wife, but she escaped in the direction to the bridge, they pursued her on horses and she decided to jump and perish instead, but the devil shows himself to the Turks and saved the girl?
3. Nobody was able to build the bridge over high (at this time water), a local builder was appointed and he made the deal with the devil if he manage to build devils face in the bridge but hard to see Devil will help with construction, Dimitar (was the name) hid the face of a Satan so it's visible only between 11 and 12 o'clock from specific angle?
I do not know which one made the name but it stays till now