Krivus (Bulgarian: Кривус) is a medieval fortress in the Rhodope Mountains of southern Bulgaria rising over a high hill on the meanders of the river Arda.

[1][3] The fortress raises on a promontory with steep slopes on the right bank of the Arda, surrounded from the north, west and south by a meander of the river.

The steep rocky slopes descending to the north and south of the citadel do not allow a would-be attacker to bypass it and strike a more unprotected part of the fortress.

It is 1.75 m thick and encloses a highly fractured space with a length of 130 m and a maximum width of 24 m.[2] Its northern section can be clearly traced, ending in the west with the remains a building raised above sheer cliffs, perhaps a tower.

[2] He records that in 1254, following the recent loss of the lands in the Rhodope Mountains to the Nicaean Empire, the Bulgarian emperor Michael II Asen led a successful campaign in the region.

Akropolites wrote: "He [Michael II Asen] descended from the Haemus and when he crossed the Evros, in a short time subjugated huge territory and took many towns without an effort.