 Complete the following phrase:  The Tsebelda fortress is an architectural complex consisting of ruined towers, Christian chapels, a palace, necropolis, and several other structures. It is erected on two cliffs more than 400 m high above the Kodori river gorge. The extant structures at Tsebelda are identified with the TsibiliumTzibile of the Classical authors, such as Procopius of Caesarea. It appears to have been a chief fortress in Apsilia, a vassal principality of the Lazic kingdom in the 6th century. The fortress dominated the confluence of three major routes from the northern Eurasian steppe on their way to the Black Sea. Around 550, during the 