A severe earthquake in 791 damages Tabriz,…

The Franks, campaigning in areas of present Austria and Slovenia, meet with little resistance due to drought and famine in lands controlled by the Avars, Bulgars and Slavs, but ninety percent of Charles's horses, which in 791 carry their riders as far as Gyõr, on the Moson arm of the Danube, perish of famine.

Charles, King of the Franks, having made the Bavarian ducal residence of Ratisbon (Regensburg) his base, conducts several campaigns, partly under his own command, against the Avar kingdom (in modern Hungary and Upper Austria), who have dominated the middle basin of the Danube River throughout most of the seventh and eighth centuries.

From 791, the Franks war against the Avars, who control the central Danube River valley and have over the past centuries acquired a vast hoard of gold and silver plundered or extorted largely from Constantinople's holdings.

Constantine VI, In order to distract the Bulgarian attention from Macedonia, starts a campaign in northern Thrace in April 791.

The armies meet near the fortress of Provat (twenty kilometers east of Adrianople) and the imperial forces are forced to retreat but their defeat is not decisive.

Challenges to the Abbasids are not long in coming; of particular significance is the establishment, in 789, of the first independent Shi'ite dynasty, in present-day Morocco, by Idris ibn 'Abd Allah ibn Hasan II, who had fled after participating in an unsuccessful uprising near Mecca.

Isa'q ibn 'Abd al-Samid, chief of the powerful tribal confederation of the Awraba Berbers of Volubilis, desired to consolidate his authority in northern Morocco by giving his rule an Islamic religious character, and for that purpose had invited Idris, a sharif (descendant of the Prophet Muhammad) then living in Tangier, to settle at his seat of government in Waila (Oulili).

Recognized as imam Idris I of the Awr'ba, he is assassinated by agents of the 'Abbasids in 791.

The Abdication of King Bermudo I After the Battle of Burbia (791 CE)

In his attempt to annex the Kingdom of Asturias, the Umayyad emir organizes two military campaigns:

• One army is tasked with conquering Galicia.
• The other is sent to subdue the western Basque lands.

The Battle of Burbia and Bermudo’s Defeat

Forced to defend against the Arab-Berber invasion of Álava and Galicia, King Bermudo I leads his forces into battle but suffers defeat at the Battle of the Burbia River—likely in El Bierzo—in 791 CE.

While Christian sources do not explicitly name his opponents, the battle appears to be the first major engagement in a series of aggressive Umayyad campaigns against Asturias in the 790s. Muslim chronicles, including Ibn al-Athir and al-Maqqarī, identify the Umayyad commander at Burbia as Yūsuf ibn Bukht.

Bermudo’s Abdication and Legacy

Following his defeat, Bermudo abdicates the throne. The Chronicle of Alfonso III states that he did so voluntarily, "because he was (or remembered he was) a deacon." However, it is also possible that he was forced to abdicate, as was common among Visigothic kings who demonstrated military inadequacy.

Despite his short reign, Bermudo is remembered as a merciful and pious ruler, described in the Chronicle of Albeldaas a "generous and illustrious man."

Succession and Later Life

After Bermudo’s abdication, he is succeeded by Alfonso II. He leaves behind a son, Ramiro I, who will later reign as King of Asturias.

Bermudo reportedly lives for many years after stepping down, possibly as a monk, and maintains good relations with his successor, Alfonso II.

Constantine foolishly allows Irene to return to court in January 792 and even to resume her position as co-ruler.

A hollow semblance of friendship is maintained between mother and son, but the rival factions remain.

Once in control of the state, Constantine proves incapable of sound governance.

His army is defeated by the Arabs, and …

…Constantine himself suffers a humiliating defeat at the hands of Kardam of Bulgaria in the 792 Battle of Marcellae.

The Bulgarians had built ramparts blocking the roads to the Rish Pass and the capital Pliska.

The emperor did not dare to attack for several days but by the end of July he was persuaded by "false astrologists" (according to the Byzantine chronicler Theophanes the Confessor) that the stars boded victory and attacked.

Before the beginning of the battle, while awaiting the imperial assault, the Bulgarian ruler secretly placed part of his cavalry behind the hills surrounding the battlefield.

Due to the rugged terrain the advancing imperial army breaks its order.

Taking advantage of this mistake, Kardam orders a counterattack that brings the Bulgarians a great success.

The Bulgarian cavalry goes around the imperial army and cuts their way back to their fortified camp and the fortress of Marcellae.

The Bulgarians take the supplies, the treasury and the tent of the emperor.

They chase Constantine VI to Constantinople, killing a great number of soldiers.

Many imperial commanders and officers perish in the battle.

A weapon called arkani is used by the Bulgarians in this battle: the arkani consists of a long pole with an attachment similar to a lasso at one end.

It is an excellent weapon against cavalry as the rider can easily be pulled out of the saddle by a skilled warrior armed with the arkani.

After the defeat, Constantine VI has to conclude peace with Kardam and has to pay tribute.

Avar co-rulers Kaghan and Yugrush die in 792 at the hands of their own men, who blame them for the drought and famine.

Subsequently, Avar leaders vie for control, and internal dissent troubles the Avar state.

Irene's iconodule policies alienate many among the themal troops, who are still loyal to the memory of the great warrior emperor, Constantine V. In an effort to maintain her popularity among the monkish defenders of the icons and with the population of Constantinople, she rebates taxes to which these groups are subject; she also reduces the customs duties levied outside the port of Constantinople, at Abydos and Hieros.

The consequent loss to the treasury weighs even more severely since victories won by the Arabs in Asia Minor in 781 and by the Bulgarians in 792 have led both peoples to demand and receive tribute as the price of peace.

A movement develops in favor of his Constantine’s uncle, the Caesar Nikephoros.

Constantine has his uncle's eyes put out and the tongues of his father's four other half-brothers cut off.

His former Armenian supporters revolt after he blinds their general Alexios Mosele.

He crushes this revolt with extreme cruelty in 793.

The Umayyad general Abd-al-Màlik ibn Abd-al-Wàhid ibn Mughith is more fortunate on his approach to Carcassonne, where he defeats Louis the Pious' Carolingian mentor William of Orange.

However, surprisingly, the expedition does not advance deeper into Carolingian territory, but results in hefty loot and numerous slaves, which in turn provide the funds to expand the Great Mosque of Cordoba and build many mosques.