Patmos (Bulgarian: Патмос) is a medieval fortress in the Rhodope Mountains of southern Bulgaria rising over a promontory near the confluence of the rivers Arda and Borovitsa.

Patmos is located on a hill over the mouth of the river Borovitsa and left bank of the Arda at the westernmost end of the modern Kardzhali Reservoir.

The nearest villages are Borovitsa to the south and Doyrantsi to the north, belonging to the Ardino Municipality of Kardzhali Province.

[1] Within the citadel are the ruins of a large, three-nave, three-apsed church without a vestibule and with a length of 13 m and a width 11.5 m. It is built of treated stones, joined with white mortar.

[1] North of the church are the remains of a rectangular building with a length of 10.8 m and a width 4 m, built of rubble stone and joined with white mortar.