Abu Yusuf Yakub al-Mansur (reigned 1184-1199) was the third caliph of the Almohad dynasty and the victor against the Spanish Christians at the battle of Alarcos. A
Abu Yusuf served as vizier of the Almohad empire during the reign of his father, Abu Yakub Yusuf (1162-1184), and at his death was chosen as his successor as Yakub I. Having gained considerable practical experience as an administrator in the vizierate, Yakub kept firm control of the state in his own hands, continuing the Almohad tradition of active leadership in religious affairs and vigorous military campaigns against the enemies of the state.
The first part of Yakub's reign was spent in repelling an offensive against Almohad territory in North Africa launched by the Banu Ghaniya, the Sanhaja Berbers who had continued Berber rule on the Balearic Islands. The attack came in 1185 against the eastern holdings of the Almohads on the Algerian coast and resulted in the capture of Bougie, Algiers, and other towns. The Almohad army sent by Yakub regained the Algerian possessions in 1186, and the Banu Ghaniya retreated into Ifrikiya (Tunisia). Yakub himself led an army into Ifrikiya and in 1187 defeated the Banu Ghaniya, temporarily restoring the area to the Almohad Empire. However, upon his withdrawal to Morocco and the diversion of his efforts to Spain, the Banu Ghaniya soon succeeded in challenging Almohad sovereignty in the east, which was too far removed from the seat of Almohad power to keep under permanent control without a large army of occupation.
In Spain, Yakub's military success was equally spectacular and equally ephemeral; here, as in North Africa, the Almohad campaign was a response to the invasion of their territory, though in Spain the response amounted to holy war since the invaders were Christians, led by Alfonso VIII of Castile. Between 1190—when Yakub crossed into Spain—and 1195, the fighting was inconclusive and was checked by a loose armistice agreement. But in 1195 the great battle for which Yakub is famous in Islamic history took place at Alarcos, where he won a stunning victory over the Christians and temporarily halted their advance into Moslem Spain. This battle was followed by forays led by Yakub into Christian territory, which were ended by a two-year truce when he withdrew to Morocco.
Yakub sponsored religious activities, both scholarly and popular, and built many civil and religious edifices in Spain and Morocco. In the last year of his life, weakened from an illness which had befallen him on a trip to Spain, he devoted himself wholly to piety, leaving the affairs of state to his son whom he appointed as his successor.
There is no detailed biographical study of Yakub. His role in Almohad history is discussed in Henri Terrasse, History of Morocco (2 vol., 1949-1950; trans., 1 vol., 1952). There are also chapters on the Almohads in Eleanor Hoffman, Realm of the Evening Star: A History of Morocco and the Lands of the Moors (1965), and in Nevill Barbour, Morocco, (1965). In English, the standard comprehensive work on Arabic history is Philip K. Hitti, History of the Arabs: From the Earliest Times to the Present (1937; 8th ed. 1963). For works that discuss Yakub in relation to Spanish history see S. M. Imamuddin, A Political History of Muslim Spain (1961), and W. Montgomery Watt, A History of Islamic Spain (1965).