Azerbaijan. (As of September 2018, Turkey maintains that the border will remain closed until Armenia ends its occupation). Construction on a new line, the Kars–Tbilisi–Baku railway, intended to connect Turkey with Georgia and Azerbaijan, began in 2010. The line became operational on October 30, 2017. The line connects Kars to Akhalkalaki in Georgia, from where trains will continue to Tbilisi, and Baku in Azerbaijan. Places of interest Kars Citadel The Castle of Kars (), also known as the Citadel, sits at the top a rocky hill overlooking Kars. Its walls date back to the Bagratuni Armenian period (there is surviving masonry on the north side of the castle) but it probably took on its present form during the thirteenth century when Kars was ruled by the Zak'arid dynasty. The walls bear crosses in several places, including a Khachkar with a building inscription in Armenian on the easternmost tower, so the much repeated statement that Kars castle was built by Ottoman Sultan Murad III during the war with Persia, at the close of the sixteenth century, is inaccurate. However, Murad probably ordered the reconstruction of much of the city walls (they are similar to those that the Ottoman army constructed at Ardahan). During the eighteenth century, at the Battle of Kars (1745), a crushing defeat was inflicted upon the Ottoman army by the Persian conqueror, Nader Shah, not far from the city of Kars. By the nineteenth century the citadel had lost most of its defensive purpose and a series of outer fortresses and defensive works were constructed to encircle Kars – this new defensive system proved particularly notable during the Siege of Kars in 1855. Other historical structures Below the castle is a mosque, formerly the Armenian church known as Surb Arak'elots, the Church of the Holy Apostles. Built in the 930's, it has a tetraconch plan (a square with four semicircular apses) surmounted by a spherical dome on a cylindrical drum. On the exterior, the drum contains bas-relief depictions of twelve figures, usually interpreted as representing the Twelve Apostles. The dome has a conical roof. The church was converted to a mosque in 1579, and then converted into a Russian Orthodox church in the 1880s. The Russians built porches in front of the church's three entrances, and an elaborate clocktower (now demolished) next to the church. The church was used as a warehouse from the 1930s, and it housed