Alcántara (älkänˈtärä) [key], town (1990 pop. 2,213), Cáceres prov., W Spain, in Extremadura, near the Tagus River. A fine Roman bridge (Arabic al-kantara ) built (A.D. 105–106) in honor of Emperor Trajan and the ruins of the convent and church of the Knights of Alcántara are located in the town. The Order of Alcántara, one of the great military religious orders of Spain, established its seat in the town in the 13th cent. after the expulsion of the Moors and enjoyed a period of great splendor (13th–14th cent.).