One of the main protective Rhodopean fortresses – the Krichim Fortress, is 7 km away from the lakes. It was built on an inaccessible pinnacle, which had originally had a B.C. Thracian fortification built on it, replaced by a Byzantine fortress with an area of 20 decares, and then a fortress from the period of the Second Bulgarian State. The walls still preserved are 150 cm thick and 4 m tall, and surround the highest part of the rock. The foundations of the buildings can still be seen, as well as a water reservoir. The fortress played an important part in the defense of the Rhodopes, it often changed its rulers, and it was mentioned many times by the ancient annalists. Several hundred meters away is the Asenov Kamak (Asen’s Stone), which has an inscription on it, engraved by Ivan Asen II after he conquered the fortress in 12th century. Even now it is in perfect condition and can easily be read. This was the stone where Tsar Asen was sitting when he took over Krichim.