The Principality of Achaea was a feudal state established in the early 13th century in the Peloponnese region of Greece. It emerged after the Fourth Crusade, when the Latin Empire was formed, and was ruled by Frankish nobles. The principality played a significant role in the political landscape of medieval Greece, serving as a center for trade and culture. The principality's capital was the city of Patras, and it was known for its castles and fortified towns. It eventually fell under the control of the Ottoman Empire in the 15th century, marking the end of its influence in the region.