The Battle of Tours followed two decades of Umayyad conquests in Europe which had begun with the invasion of the Visigothic Christian kingdoms of the Iberian Peninsula in 711. These were followed by military expeditions into the Frankish territories of Gaul, former provinces of the Roman Empire. Umayyad military campaigns reached northward into Aquitaine and Burgundy, including a major engagement at Bordeaux and a raid on Autun. Charles's victory is widely believed to have stopped the northward advance of Umayyad forces from the Iberian Peninsula and to have preserved Christianity in Europe during a period when Muslim rule was overrunning the remains of the Byzantine and Persian Empires.
Most historians assume that the two armies met where the rivers Clain and Vienne join between Tours and Poitiers. The number of troops in each army is not known. The Mozarabic Chronicle of 754, a Latin contemporary source which describes the battle in greater detail than any other Latin or Arabic source, states that "the people of Austrasia [the Frankish forces], greater in number of soldiers and formidably armed, killed the king, Abd ar-Rahman", which agrees with many Arab and Muslim historians. However, virtually all Western sources disagree, estimating the Franks as numbering 30,000, less than half the Muslim force.
Some modern historians, using estimates of what the land was able to support and what Martel could have raised from his realm and supported during the campaign, believe the total Muslim force, counting the outlying raiding parties, which rejoined the main body before Tours, outnumbered the Franks. Drawing on non-contemporary Muslim sources, Creasy describes the Umayyad forces as 80,000 strong or more. Writing in 1999, Paul K. Davis estimates the Umayyad forces at 80,000 and the Franks at about 30,000, while noting that modern historians have estimated the strength of the Umayyad army at Tours at between 20–80,000. However, Edward J. Schoenfeld, rejecting the older figures of 60–400,000 Umayyads and 75,000 Franks, contends that "estimates that the Umayyads had over fifty thousand troops (and the Franks even more) are logistically impossible." Similarly, historian Victor Davis Hanson believes both armies were roughly the same size, between 20,000 and 30,000 men.:141
Contemporary historical analysis may be more accurate than the medieval sources, as the modern figures are based on estimates of the logistical ability of the countryside to support these numbers of men and animals. Both Davis and Hanson point out that both armies had to live off the countryside, neither having a commissary system sufficient to provide supplies for a campaign. Other sources give the following estimates: "Gore places the Frankish army at 15,000–20,000, although other estimates range from 30,000 to 80,000. In spite of wildly varying estimates of the Muslim force, he places that army as around 20,000–25,000. Other estimates also range up to 80,000, with 50,000 not an uncommon estimate." 
Losses during the battle are unknown, but chroniclers later claimed that Charles Martel's force lost about 1,500 while the Umayyad force was said to have suffered massive casualties of up to 375,000 men.Liber Pontificalis for Duke Odo the Great's victory at the Battle of Toulouse (721). Paul the Deacon reported correctly in his History of the Lombards (written around 785) that the Liber Pontificalis mentioned these casualty figures in relation to Odo's victory at Toulouse (though he claimed that Charles Martel fought in the battle alongside Odo), but later writers, probably "influenced by the Continuations of Fredegar, attributed the Muslims casualties solely to Charles Martel, and the battle in which they fell became unequivocally that of Poitiers." The Vita Pardulfi, written in the middle of the eighth century, reports that after the battle 'Abd-al-Raḥmân's forces burned and looted their way through the Limousin on their way back to Al-Andalus, which implies that they were not destroyed to the extent imagined in the Continuations of Fredegar.
However, these same casualty figures were recorded in the
The invasion of Hispania, and then Gaul, was led by the Umayyad dynasty (Arabic: بنو أمية banū umayya / الأمويون al-umawiyyūn also "Umawi"), the first dynasty of Sunni caliphs of the Sunni Islamic empire after the reign of the Rashidun Caliphs (Abu Bakr, Umar, Uthman, and Ali) ended. The Umayyad Caliphate, at the time of the Battle of Tours, was perhaps the world's foremost military power. Great expansion of the Caliphate occurred under the reign of the Umayyads. Muslim armies pushed east across Persia and west across North Africa through the late 7th century.
In 711–18, Tariq ibn Ziyad led forces across the Strait of Gibraltar to conquer the Visigothic Kingdom of Hispania. The Muslim empire under the Umayyads was now a vast domain that ruled a diverse array of peoples. It had destroyed what had been the two foremost military powers, the Sasanian Empire, which it absorbed completely, and the greater part of the Byzantine Empire, including Syria, Armenia and North Africa, although Leo the Isaurian stemmed the tide when he defeated the Umayyads at the Battle of Akroinon (739), their final campaign in Anatolia.
The Frankish realm under Charles Martel was the foremost military power of western Europe. During most of his tenure in office as commander-in-chief of the Franks, it consisted of north and eastern France (Austrasia, Neustria and Burgundy), most of western Germany, and the Low Countries (Luxembourg, Belgium and the Netherlands). The Frankish realm had begun to progress towards becoming the first real imperial power in western Europe since the fall of Rome. However, it continued to struggle against external forces such as the Saxons, Frisians, and other opponents such as the Basque-Aquitanians led by Odo the Great (Old French: Eudes), Duke over Aquitaine and Vasconia.
Umayyad conquests from Hispania
The "Age of the Caliphs
", showing Umayyad dominance stretching from the Middle East to the Iberian Peninsula, including the port of Narbonne
, c. 720
Modern-day French borders. Septimania runs along the Mediterranean (southeast) coast from the Spanish border, and Aquitaine is along the Atlantic (west) coast running north from Spain.
The Umayyad troops, under Al-Samh ibn Malik al-Khawlani, the governor-general of al-Andalus, overran Septimania by 719, following their sweep up the Iberian Peninsula. Al-Samh set up his capital from 720 at Narbonne, which the Moors called Arbūna. With the port of Narbonne secure, the Umayyads swiftly subdued the largely unresisting cities of Alet, Béziers, Agde, Lodève, Maguelonne, and Nîmes, still controlled by their Visigothic counts.
The Umayyad campaign into Aquitaine suffered a temporary setback at the Battle of Toulouse. Duke Odo the Great broke the siege of Toulouse, taking Al-Samh ibn Malik's forces by surprise. Al-Samh ibn Malik was mortally wounded. This defeat did not stop incursions into old Roman Gaul, as Moorish forces, soundly based in Narbonne and easily resupplied by sea, struck eastwards in the 720s, penetrating as far as Autun in Burgundy in 725.
Threatened by both the Umayyads in the south and by the Franks in the north, in 730 Odo allied himself with the Berber commander Uthman ibn Naissa, called "Munuza" by the Franks, the deputy governor of what would later become Catalonia. To seal the alliance, Uthman was given Odo's daughter Lampagie in marriage, and Moorish raids across the Pyrenees, Odo's southern border, ceased. However, the next year, the Berber leader killed the bishop of Urgell Nambaudus and detached himself from his Arabs masters in Cordova. Abdul Raḥman in turn sent an expedition to crush his revolt, and next directed his attention against Uthman's ally Odo.
Odo collected his army at Bordeaux, but was defeated, and Bordeaux plundered. During the following Battle of the River Garonne, the Chronicle of 754 commented that "God alone knows the number of the slain". The Chronicle of 754 continues, saying they "pierced through the mountains, trampled over rough and level ground, plundered far into the country of the Franks, and smote all with the sword, insomuch that when Eudo came to battle with them at the River Garonne, he fled."
Odo's appeal to the Franks
Odo, who despite the heavy losses was reorganizing his troops, gave the Frankish leader notice of the impending danger knocking on the heartland of his realm, and appealed to the Franks for assistance, which Charles Martel only granted after Odo agreed to submit to Frankish authority.
It appears that the Umayyads were not aware of the true strength of the Franks. The Umayyad forces were not particularly concerned about any of the Germanic tribes, including the Franks, and the Arab chronicles of that age show that awareness of the Franks as a growing military power only came after the Battle of Tours.
Further, the Umayyads appear not to have scouted northward for potential foes, for if they had, they surely would have noted Charles Martel as a force to be reckoned with in his own account, because of his growing domination of much of Europe since 717.
Umayyad advance towards the Loire
In 732, the Umayyad advance force was proceeding north towards the Loire River, having outpaced their supply train and a large part of their army. Having easily destroyed all resistance in that part of Gaul, the invading army had split off into several raiding parties, while the main body advanced more slowly.
The Umayyads delayed their campaign late in the year probably because the army needed to live off the land as they advanced. They had to wait until the area's wheat harvest was ready and then until a reasonable amount of the harvested and stored.
The reason why Odo was defeated so easily at Bordeaux and Garonne, but had won 11 years earlier at the Battle of Toulouse is simple. At Toulouse, Odo managed a surprise attack against an overconfident and unprepared foe. The Umayyad forces were mostly infantry, and what cavalry they did have were never mobilized. As Herman of Carinthia wrote in one of his translations of a history of al-Andalus, Odo managed a highly successful encircling envelopment which took the attackers totally by surprise – the result was a chaotic slaughter of the Muslim forces.
At Bordeaux and again at Garonne, the Umayyad forces were mostly cavalry and had the chance to mobilize, which led to the devastation of Odo's army. Odo's forces, like other European troops of that era, lacked stirrups, possibly explaining which resulted in no heavy cavalry at that time. Most of their troops were infantry. The Umayyad heavy cavalry broke Odo's infantry in their first charge, and then slaughtered them as they broke and ran.
The invading force went on to devastate southern Gaul. A possible motive, according to the second continuator of the Chronicle of Fredegar, was the riches of the Abbey of Saint Martin of Tours, the most prestigious and holiest shrine in western Europe at the time. Upon hearing this, Austrasia's Mayor of the Palace, Charles Martel prepared his army and marched south, avoiding the old Roman roads, hoping to take the Muslims by surprise.