As indicated at the start of the discussion of the area during the Middle Ages, despite its history as a fortified border from the tenth century, the area was unimportant until the thirteenth. The King of the (now united) Kingdom of Castile and Leon, Alphonse VII (1126–1157), made a series of internal territorial changes that transferred Leonese territories to the Crown of Castille: specifically, The Tierra de Campos to the north of the Duero, an area valued at the time for its riches, and the "alfoz de Medina del Campo" (to the south of the Duero), a poor and sparsely populated zone, although it possessed a certain strategic value in terms of the defense of the passes of the Duero valley. During the time of the union of the two crowns, the question of who owned these areas was of little importance; however, upon the death of Alphonse VII and the division of his possession amongst his sons, continuous conflicts arose over the control of the area, especially "Tierra de Campos", but also, though less importantly, over the area of Medina del Campo.