The Umayyad Caliphate achieved notable success in establishing diplomatic relations with neighboring countries. One of the most well-known diplomatic events between Islam and Christianity during the Umayyad era was a peace treaty concluded between Caliph Hazrat Muawiyah and Byzantine Emperor Constantine IV in 58 AH / 687 CE, after the failed siege of Constantinople. Following this, delegations were repeatedly sent from the Byzantine Empire to Damascus to discuss and evaluate Muawiyah’s intentions and willingness to strengthen relations between the two governments. As a result, limited diplomatic exchanges took place between them.
During the Abbasid era, political relations between the Abbasid Caliphate and the Byzantine Empire fluctuated, sometimes stable and sometimes tense. Numerous wars, treaties, and political events occurred between the two, and in many instances, diplomatic missions and negotiations were held. These continuous political and diplomatic interactions between a major Islamic state and its Christian neighbor in the East were natural occurrences.
Diplomatic exchanges and negotiations were conducted according to the customs and legal frameworks of that era and were usually held in the capital city of the more powerful state.
These relations significantly influenced the political orientation of Islam toward Christianity and vice versa. During times when the East was at the height of power and grandeur, influence flowed from East to West, as it was often the West that sought peace with a powerful Islam.
With the rise of the Abbasid Caliphate and the consolidation of its foundations—and simultaneously with the establishment of a new Umayyad state in al-Andalus—Baghdad and Cordoba became political hubs for East–West Islamic–Christian relations. At the same time, the emergence of France as the strongest power in Western Europe diverted the attention of Western nations from the Eastern Roman (Byzantine) Empire, becoming a new factor in the political pull between East and West.
During the caliphate of al-Mansur, the second Abbasid caliph, France sought to establish political relations with the Muslim caliph in the East, thereby creating a new global balance. Pepin, the king of France, sent his envoys to Baghdad to meet with al-Mansur.
French historians record the dispatch of this delegation in 765 CE / 148 AH. According to reports, the French envoys spent some time in Baghdad and returned to France three years later, accompanied by representatives from the caliph. They arrived at the palace in Marseille.
The King of France warmly welcomed the caliph’s envoys and invited them to spend the winter in Metz, the royal court of France at the time. He later invited them to relax at the palace of Selz, located by the river Nehler. Afterward, the Abbasid envoys returned to Baghdad via the port of Marseille, carrying gifts from the King of France.
These political exchanges between the Abbasid Caliphate and the King of France continued for a long time and peaked during the reign of Harun al-Rashid. According to French sources, numerous diplomatic missions and correspondences took place between the two sides.
French chronicles state that the Abbasid Caliphate sought rapprochement and contact with France in the far West, due to the particular situation in Islamic Spain (al-Andalus). ‘Abd al-Rahman, the first Umayyad caliph of al-Andalus, had seized control of the region and established a powerful state. The Abbasids, observing this new Umayyad entity cautiously, were concerned. Similarly, the King of France had his own motives for collaboration with the Abbasid East, as he was alarmed by the growing power of Islam and its consolidation south of the Pyrenees, and felt obliged to defend the Church and contain the spread of Islam into southern France.
French historians mention that friendly relations between Baghdad and France continued even after the deaths of Harun al-Rashid and Charlemagne. Al-Ma’mun, son of Harun, sent another envoy to Louis, son of Charlemagne and king of France, to strengthen ties between the two states.
French historians note that Harun played a significant role in preventing Muslim pirates from attacking the French and Italian coasts, and they report that Pope Leo III, after Harun’s death, wrote to Charlemagne, stating that the lack of respect shown by Muslim pirates to the French coasts was due to the death of Harun, who had lost his influence over them.
At a time when both the Umayyad state in al-Andalus and the Byzantine Empire were seen as rivals and enemies of the Abbasid Caliphate, these two powers decided to form a peace pact, thereby establishing friendly relations. As a result, significant diplomatic exchanges and correspondences occurred between the Umayyad rulers of Spain and the Caesars of Constantinople.
In 836 CE / 225 AH, the Byzantine emperor Theophilos sent a delegation with gifts to the court of ‘Abd al-Rahman ibn al-Hakam, the ruler of al-Andalus. In a letter, he invited ‘Abd al-Rahman to enter into an alliance and encouraged him to reclaim the eastern territories once held by his Umayyad ancestors. Theophilos also reprimanded al-Ma’mun and his brother al-Mu‘tasim for attacking Byzantine territories, referring to them with insulting titles in his letter.
‘Abd al-Rahman ibn al-Hakam replied by sending valuable gifts through his envoy Yahya al-Ghazal, a prominent official and renowned poet. Thus, a bond of friendship and alliance was established between the two sides.
However, the relationship between the Byzantine emperor and the ruler of al-Andalus remained mostly limited to correspondence and formalities, as the successors of ‘Abd al-Rahman I (al-Dakhil) continued his policy of focusing on securing the Iberian Peninsula and strengthening the Umayyad state within it. This policy persisted until the reign of ‘Abd al-Rahman al-Nasir, who, in light of the successes and events of his time, found it necessary to involve himself in Maghreb (North African) affairs.
Returning to the topic of Abbasid–Byzantine relations—which symbolized interaction between Islam and Christianity at the time—in the late 8th century CE, a clever and determined woman named Irene, the wife of Emperor Leo IV, ascended to power in the Byzantine Empire. She ruled as regent for her young son Constantine, and when he grew older and sought power, she opposed him, defeated him, and imprisoned him.
The Muslims capitalized on these internal Byzantine conflicts, launching military campaigns in Asia Minor, reaching as far as the Bosphorus.
At that time, Harun al-Rashid, then the heir apparent of his father al-Mahdi, personally led many of these campaigns. Eventually, Irene was compelled to seek peace and sent envoys to Harun, who was encamped with his forces near the Bosphorus. Harun accepted her request.
A treaty was concluded between the two sides, in which Irene pledged to pay an annual tribute of 70,000 dinars to the Abbasid Caliphate. To mark the occasion, Harun and the Roman queen exchanged royal gifts. (166 AH / 783 CE)
When Harun succeeded his father as caliph, Irene had already been deposed, and Nikephoros, the former treasurer (called “Yaqur” by Arab historians), had seized control of Constantinople.
As soon as he came to power, Nikephoros declared his hostility toward the Abbasid court and renounced the treaty previously signed with Irene, refusing to pay the tribute. He then sent envoys to Harun with a strongly worded letter, demanding that the caliph respect his past commitments to Byzantium or prepare for war.
Harun, enraged by the letter, led a massive army into Asia Minor and occupied the region up to Heraclea (806 CE). Nikephoros was forced to sue for peace, and Harun sent another envoy to finalize the new treaty.
A new agreement was reached, in which the Byzantine emperor pledged to restore destroyed military fortresses, to pay an annual tribute of 30,000 dinars, and to send three special gold coins—one from himself and two from his son—as a sign of submission to the Caliph of the Muslims.
