Church of the Forty Martyrs at Tarnovo
The Church of the Forty Martyrs was built by John Asen II to celebrate his victory over Theodore Komnenos Doukas at Klokotnica in 1230. It contains a Greek inscription of Omurtag and a Slavic inscription of John Asen II. It perhaps has the tomb of St. Sava of Serbia, who died in Tarnovo in 1251.
Map of Tarnovo
Byzantine Architecture by Cyril Mango
Oxford Dictionary of Byzantium edited by Alexander Kazhdan