Meanwhile, the takeover of the southern fringes of Al-Andalus by Abd ar-Rahman I in 756 was opposed by Yusuf ibn Abd al-Rahman, autonomous governor ("wāli") or king ("malik") of al-Andalus. Abd ar-Rahman I expelled Yusuf from Cordova, but it took still decades for him to expand to the north-western Andalusian districts. He was also opposed externally by the Abbasids of Baghdad who failed in their attempts to overthrow him. In 778, Abd al-Rahman closed in on the Ebro valley. Regional lords saw the Umayyad emir at the gates and decided to enlist the nearby Christian Franks. According to Ali ibn al-Athir, a Kurdish historian of the 12th century, Charlemagne received the envoys of Sulayman al-Arabi, Husayn, and Abu Taur at the Diet of Paderborn in 777. These rulers of Zaragoza, Girona, Barcelona, and Huesca were enemies of Abd ar-Rahman I, and in return for Frankish military aid against him offered their homage and allegiance.