During these years, in which he had been fighting the Moors, Affonso Henriques had observed the terms of the Treaty of Zamora, and had prudently avoided all interference in the affairs of Spain; but the death of his cousin, the Emperor Alfonso, in 1157, which left him the oldest and most famous warrior in the peninsula, seems to have tempted him to abandon this prudent policy. The Emperor had divided his kingdoms, leaving Castile to his son Sancho, and Leon and Gallicia to his son Ferdinand, a division which also seems to have tempted Affonso to believe he could play a part in Spanish affairs. His alliance was sought on all sides, and in January, 1160, he betrothed his eldest daughter, Donna Matilda, to Raymond Berenger, heir to the throne of Aragon; and a little later in the same year he promised his second daughter, Donna Urraca, to King Ferdinand; and concluded the Treaty of Cella Nova, by which it was agreed that each monarch should prosecute his wars against the Moors independently, and that the course of the Guadiana should be the limit between their respective lines of conquest. This treaty was, undoubtedly, caused by the fact that the Moors in Africa had again become united under the rule of the Almohade caliph, Abd-el-Mumin, and that a great invasion of Spain by the Mohammedans was to be expected.
This invasion occurred in the very next year, 1161. Abd-el-Mumin crossed the straits of Gibraltar with eighteen thousand tried Almohade soldiers, and after subduing the independent Mohammedan em[=i]rs, inflicted upon Affonso Henriques his first real defeat, and drove him back to Lisbon and Santarem. The death of Abd-el-Mumin in 1163 again changed the aspect of affairs. A disputed succession kept the Almohade warriors busy in Africa, and independent bands of "salteadors," who were little better than brigands and free lances, began to establish themselves as petty feudal princes in the various cities and districts of the Alemtejo, the province south of the Tagus, which now became the battle-ground between the Christians and the Moors. Affonso Henriques let them do as they liked; he had a greater ambition, and as he had formerly schemed and planned to take Santarem, Lisbon, and Alcacer do Sal, he now cast his eyes upon the great city of Badajoz, although it lay upon the eastern side of the Guadiana which he had agreed to leave to the King of Leon. With this object in view he took Beja in 1162, Truxillo and Evora in 1165, and Caceres in 1166, thus gradually working up to the city which he coveted. King Ferdinand was not the man to allow these breaches of treaty to pass unnoticed, and founded the city of Ciudad Rodrigo, to command and threaten the north-eastern districts of Portugal.