Alexios I (1081-1118)
The reign of Alexios is well-documented due to the survival of the Alexiad, written by his daughter Anna Komnene, which details all of the events of his reign, albeit with a bias towards Alexios. Upon ascension, Alexios inherited a much weakened empire that was almost immediately beset by a serious invasion from the Normans of Southern Italy. The Normans used the deposition of the previous emperor Michael as the casus belli to invade the Balkans. Alexios did not have a strong enough army to successfully resist the invasion at first and suffered a grave defeat at the Battle of Dyrrachium (1081), which allowed Robert Guiscard and his son Bohemond to occupy much of the Balkans.
After this victory, the Normans took Dyrrhachium in February 1082 and advanced inland, capturing most of Macedonia and Thessaly. Robert was then forced to leave Greece to deal with an attack on his ally, the Pope, by the Holy Roman Emperor, Henry IV. Robert left his son Bohemond in charge of the army in Greece. Bohemond was initially successful, defeating Alexius in several battles, but was defeated by Alexius outside Larissa. Forced to retreat to Italy, Bohemond lost all the territory gained by the Normans in the campaign. This victory began the Komnenian restoration.
Shortly after the death of Robert in 1185, the Pechenegs, a nomadic group from north of the Danube, invaded the empire with a force 80,000 strong. Realizing that he would not be able to defeat the Pechenegs by conventional means, Alexios I allied with another nomadic group, the Cumans, to aid him, which resulted in the annihilation of the Pecheneg horde at the Battle of Levounion on 28 April 1091.
Shortly after this Alexios I began what was perhaps his most important action while Emperor when he called on Pope Urban II for help in combating the Muslims of Anatolia and the Levant. Particularly Alexios hoped to recover Syria and other areas that had been part of the Byzantine Empire in centuries previous. He succeeded in his attempt to rally Western European support, as a surprisingly large contingent of crusaders under Godfrey of Bouillon (among other European nobles) set off from Western Europe and journeyed through Anatolia all the way to their eventual destination of Jerusalem. While relations between crusaders and Byzantines were not always cordial, the coordination between the two armies was instrumental in capturing many important cities in Asia Minor and eventually Jerusalem itself. Between 1097 and 1101 Alexios managed to recover Nicaea, Rhodes, Ephesus and made while also making Antioch his vassal. This brought the Empire to its largest extent in over three centuries.
In order to achieve these important military victories, however, Alexios had to resort to drastic measures in order to keep the empire financially afloat amidst so many military expeditions. He did this by melting down many Church artifacts and selling Church lands while also utilizing conscription to keep the army well-staffed. This led to a diminution of his popularity, but he was nonetheless successful in resurrecting the Byzantine Empire by the time of his death in 1118.
Read more about this topic: Komnenian Restoration