The primary historical sight in Oltu is the castle, which covers the top of a rocky outcrop. Its walls are fortified by large round towers and salients, including an imposing talus at the southwest. A circuit wall once extended from the outcrop to protect a small adjoining settlement. The medieval fortress is the result of two major periods of construction between the 7th and the 11th centuries; major repairs were undertaken by the Turkish Corps of Engineers in 1977. Atop the north tower are the remains of a Georgian hexaconch church in which a fragment of a 7th-century “bilingual” Greek-Armenian inscription was reused in the foundation. This Georgian church was built sometime between the 9th and 10th centuries. Inside the north tower is the tomb of a Muslim saint, Mişrî Zenūn. Late-antique and medieval churches as well as fortresses are located in the hills surrounding the Oltu-Penek valley at Cücürüs, Körolu, Olur, Kamhis, Sağoman, Olan, and nearby Kız.