The Duchy of Castile was a historical territory in medieval Spain, established in the 11th century. It played a significant role in the formation of the Kingdom of Castile, which later became part of modern Spain. The duchy was known for its agricultural wealth and strategic location, contributing to the region's political and economic power. The Duchy of Castile was ruled by various noble families, with the most notable being the House of Castro. Over time, it became a vital part of the Spanish crown's expansion, influencing the culture and governance of the Iberian Peninsula.