General Notes

He was born in 742 to Pepin the Short, who was Mayor of the Palace of Childeric III, the last of an ever degenerating line of Merovingian kings. In 751, with the support of the Pope, Pepin cut off Childeric's long hair, the mark of his kingship, and sent him to a monastery, arrogating to himself the royal power. He was an active ruler, imposing peace on his border-lands, and twice descending on Italy to protect the Pope from the Lombards, giving to him the duchy of Rome as his own state in the bargain.
In 768 Charlemagne and his brother Carloman succeeded to the joint rule of the Franks, but three years later Carloman died, and Charlemagne ruled supreme. He was as active as his father in defending and expanding his territories. In 773, when the Lombards were again putting pressure on the Pope, he crossed the Alps with astonishing speed and defeated the Lombards absolutely, putting their king in a monastery (now a family habit) and assuming the 'Iron' Crown of Lombardy himself.
He now began a systematic campaign to conquer the Saxons, and ten years of the most bitter fighting ensued. The Saxons discovered an able leader in Widukind, and in 782, managed to wipe out a substantial army of Franks. Charlemagne had 4,500 Saxons beheaded at Verden in retribution, and went on to celebrate 'The Nativity of Our Lord and Easter as he was wont to do,' says Einhard, his biographer. It took nearly three years to find Widukind, and he was then baptized---a clear declaration of submission; the rest of the Saxons gave little trouble in taking baptism, or obeying their new Frankish masters---they remembered Verden.
A feudal vassal of Charlemagne who should have learned a lesson from this was Duke Tassilo of Bavaria, but he preferred to behave as if he were independent of his overlord. Charlemagne gave him one chance to reform, but then found that he was plotting with his enemies, so in 788 he too was put into a monastery, and Bavaria was incorporated into the fast growing empire.
In Spain he was not so successful: he had been forced to call off his invasion in 778, for his troops were needed elsewhere, and anyway the Muslims turned out to be not as disunited as he had been told; it was in this retreat that Roland died. But in 793 the Muslims attacked over his borders, so he set up an enclave on the southern side of the Pyrenees to guard the area.
He now turned his attention to the Avars, relations of the Huns, who lived in the area of the middle Danube, and were phenomenally rich with tribute-money they had wrung from the Byzantine Emperors. Peaceful negotiations had failed to keep them from raiding Charlemagne's lands, and so he set out to conquer them. It was as hard a war as that against the Saxons, lasting from 791-9, and Charlemagne was wise to distribute the loot he gained from it to his war-weary people instead of keeping it for himself.
Since 476 there had been no Emperor in the West, and until recently the Popes had looked to the Byzantine Emperors for protection. In 800 the Pope was set upon and deposed, and Charlemagne had to go do to Rome to restore him. On Christmas Day of that year he was praying in St. Peter's when the Pope came up and crowned him as Emperor, taking him 'unawares.' Historians wrangle over the coronation of Charlemagne, and the results of their searches read like detective stories. Suffice it to say that Charlemagne must have known what was going to happen, but he was rather disturbed about the whole thing afterwards; possibly he was upset at not having the fiat of the Emperor of the East, though a woman was reigning there at the time, possibly he felt the Pope had arrogated to himself too great a part in the coronation. Certainly he kept a very healthy respect for the Byzantine Empire, though he was not a man to fear another's power: he had good relations with Haroun-al-Rashid, the Caliph of Baghdad, who sent him a white elephant, and arranged protection for pilgrims visiting Jerusalem, in the heart of Muslim territory. In a less exciting area he developed good relations also with the various Anglo-Saxons states in England; and the first commercial treaty of which we have a record in English history is a letter from Charlemagne to Offa of Mercia, then the central Anglo-Saxon state, requesting more short cloaks, but not as short as the last batch, for when one was forced by the call of nature to get off one's horse, the cloak turned out to be a very draughty affair.
Einhard's biography gives us a fine picture of Charlemagne in the prime of his life: a large pleasant looking man, with rather a weak voice, who loved all forms of exercise, but excelled in swimming. He wore the ordinary dress of his nation, objecting strongly to having to dress in Roman fashion on the two occasions Popes requested it to impress the citizens of Rome. He ate and drank moderately, but had a passion for roast meat. He loved to hear music and to listen to readings from St. Augustine's City of God; he also delighted in the old songs of his nation, which his priggish son had destroyed after his death, because they were pagan. He plainly respected learning, and loved to be surrounded by learned people, but he probably didn't get very far in his own learning; he used to keep a copy-book under his pillow (he suffered from insomnia) but he never really learned to write.
His palace at Aachen was the Versailles of the ninth century, beautiful and impressive, though it is a typically homely touch that he settled on this site because the swimming was good there, with natural hot springs to warm the water. The pictorial arts flourished under him, especially in the decoration of books, which themselves were written in the fine minuscule hand which was developed in his reign, and was to form the basis of the Renaissance italic hand. Schools were built up, modelled on the palace school, which was more of a university in that it served as a place for distinguished scholars to work, and a training ground for the sons of the nobility. Alcuin was called from England, and Peter of Pisa came, along with the best minds of the age. Monasteries built up huge libraries, and in their scriptoria multiple copies were made. By these means the riches of literature of the ancient world were preserved for the modern, and not even the destructive power of the Norsemen could entirely root out the achievement. Although the full effect of this educational revolution was not to be felt until after the death of Charlemagne, when the whole of Europe began to build great edifices of stone, and theologians and philosophers dared to reason, this was truly the Carolingian Renaissance, and owed a tremendous debt to the boundless vision and enthusiasm of Charlemagne himself.
In fact, the cultural influences of the Carolingian state were to outlast by far the state itself. Having conquered territories, Charlemagne tended to do little but install Frankish counts there, introduce his elementary form of feudalism, and then occasionally add to the legal system such laws as were necessary. He sent round groups of 'Missi Dominici' to check on the administration of the counts, and held formal assemblies each year, which provided an elementary check on what was happening all over the Empire; but it was only while his dominant personality and military might were at the head of the system that it could work---the whole Empire was ready to spring apart into fragments when this was removed. It lacked the economic organisation necessary for unity, retaining the spirit of self-sufficiency which was the hallmark of medieval regionalism.
On his death in 814, his son Louis the Pious succeeded, but on his death in 840 civil war broke out between Louis' sons, and in 843 at Verdun the Empire was divided between the three of them, one taking the western strip, one the eastern and the third taking a central strip right down from the Low Countries to half-way down Italy---Germany was to go a separate way from that of France, the Low Countries and Burgundy were to aim at separate development, and all were to have interest in what became of the Italian domains.
It is possible to place too much emphasis on the decisiveness of this treaty for the future history of Western Europe, but even so one should remember that the year before it was made when the two leaders of West and East met to make the preliminary arrangements, the one swore his oath in French and the other in German so that their followers could understand them.
The popular names for the rulers who followed in the wake of Charlemagne spell out for us the decline from greatness, Louis the Pious, Charles the Bald, Louis the Stammerer, Charles the Fat, Charles the Simple. Europe was to be divided, with disastrous results; but nonetheless people remembered the achievement of Charlemagne through the long terrible years of war and the terrible attacks from the Norsemen. They created the tradition of the Song of Roland, which was only outdone in popularity by the later re-workings of the predominantly national legends of the Germans and the Celtic lands.