The Klis Fortress is a medieval fortress situated above the village of Klis, near Split, Croatia. From its origin as a small stronghold built by the ancient Illyrian tribe Dalmatae, to a role as royal castle and seat of many Croatian kings, to its final development as a large fortress during the Ottoman wars in Europe, Klis Fortress has guarded the frontier, being lost and re-conquered several times throughout its two-thousand-year-long history. Due to its location on a pass that separates the mountains Mosor and Kozjak, the fortress served as a major source of defense in Dalmatia, especially against the Ottoman Empire. It has been a crossroad between the Mediterranean Sea and the Balkans. Since Duke Mislav of the Duchy of Croatia made Klis Fortress the seat of his throne in the middle of the 9th century, the fortress served as the seat of many Croatia’s rulers. His successor, Duke Trpimir I, is significant for spreading Christianity in the Duchy of Croatia. He expanded the Klis Fortress, and in Rižinice, in the valley under the fortress, he built a church and the first Benedictine monastery in Croatia.