The Battle of Lalakaon () or Battle of Po(r)son ()Jenkins (1987), p. 163 was fought in 863 between the Byzantine Empire and an invading Arab army in Paphlagonia (modern northern Turkey). The Byzantine army was led by emperor Michael III's uncle, Petronas the Patrician, although Arab sources also mention the presence of Michael himself, while the Arabs were led by the emir of Melitene (Malatya), Omar al-Aqta.

Omar al-Aqta was able to brush off the initial Byzantine resistance against his invasion and reach the shores of the Black Sea. The Byzantines however mobilized their forces, and the Arab army was encircled near the river Lalakaon. The subsequent battle ended in a complete Byzantine victory and the death of the emir on the field, and was followed by a successful Byzantine counter-offensive across the border. The Byzantine victories proved decisive: the main threats to the Byzantine borderlands were eliminated, and the era of Byzantine ascendancy in the East, which would culminate in the great conquests of the 10th century, had begun.

The Byzantine success had another corollary: deliverance from the constant Arab pressure of the eastern frontier allowed the Byzantine government to concentrate on affairs in Europe, and, in particular, neighboring Bulgaria. The Bulgarians were pressured into accepting the Byzantine form of Christianity, thus ensuring that this nation would come within the Byzantine cultural sphere.

Background

Byzantine-Arab border wars

Following the rapid Muslim conquests of the 7th century, the Byzantine Empire found itself confined to Asia Minor, the southern Balkan coasts and parts of Italy. As Byzantium remained the Caliphate's major infidel enemy, Arab raids (razzias) into Asia Minor continued throughout the 8th and 9th centuries. Indeed, these annual expeditions against Byzantium acquired an almost ritualized character. During that period, the Byzantines were generally on the defensive,El-Cheikh (2004), p. 162 and suffered some catastrophic defeats such as the razing of Amorium, the home city of the reigning Byzantine dynasty, in 838. With the waning of the Abbasid Caliphate's power after 842 and the rise of quasi-independent emirates beyond the Byzantine eastern frontier however, the Byzantines were more able to assert their own power.

In the 850s, the most persistent threats to the Empire were the Emirate of Melitene under Omar al-Aqta, the Emirate of Tarsos under 'Ali ibn Yahya ("the Armenian"), the emirate of Kalikala (Theodosiopolis, modern Erzurum) and the Paulicians of Tephrike under their leader Karbeas.Whittow (1996), p. 310 Melitene in particular was a major threat to Byzantium, as its location on the western side of the Antitaurus range allowed access to the Anatolian plateau. An indication of the threat posed by these states came in 860, when their combined actions turned the year into a veritable annus horribilis for the Byzantines: Omar and Karbeas raided deep into Asia Minor and returned with much plunder; they were followed shortly after by another raid by the forces of Tarsos under 'Ali, while a naval attack from Syria sacked the major Byzantine naval base at Attaleia.

Arab invasion of 863

In the summer of 863, Omar struck again, uniting his forces with 'Ali for a raid into Cappadocia,Haldon (2004), p. 133Huxley (1975), p. 448 and it is likely that a Paulician contingent under Karbeas was present as well.Kiapidou (2003)Jenkins (1987), p. 162 According to the Byzantine history of Theophanes Continuatus, the Arab army numbered 40,000 men. More modern estimates lower that number to ca. 20,000, but it still represented a large army for its time. The Arabs crossed the Cilician Gates into Byzantine territory, plundering as they went, until they reached a place near Tyana. There, for unknown reasons, the larger army of Tarsos turned back, while the emir of Melitene decided to press on alone.
On the Byzantine side, emperor Michael III had assembled his army to counter the Arab raid, and met them at a battle in an area called Mardj al-Usquf ("Bishop's Meadow") by Arab sources, a highland near Malakopea, north of Nazianzus. The battle was bloody with many casualties on both sides, but the Arabs managed to evade the Byzantines and continue their raid north into the Armeniac theme, eventually reaching the Black Sea and sacking the port city of Amisos.Haldon (2004), p. 134Treadgold (1997), p. 452

The battle

thumb|right|250px|Battle between Byzantines and Arabs. From the Madrid Skylitzes manuscript.
As soon as Michael learned of the fall of Amisos, he ordered a huge force to be assembled (the Persian historian Al-Tabari gives its size at 50,000 men) under his uncle Petronas the Patrician, the stratēgos of the Thracesian Theme. Al-Tabari records that the emperor himself assumed command of these forces, but this is not supported by Byzantine sources. However, given the bias against Michael by the historians writing during the Macedonian dynasty, this may be a deliberate omission. The forces assembled came from all over the Empire. Three separate armies were formed which converged upon the Arabs: a northern Byzantine force composed of the forces from the Black Sea themes of the Armeniacs, Bucellarians (under Nasar), Koloneia and Paphlagonia; a southern force, that had already fought at the Bishop's Meadow and had kept shadowing the Arab army, from the Anatolic, Opsician and Cappadocian themes, as well as the kleisourai of Seleucea and Charsianon; and the western force, under Petronas himself, comprising the men of the Macedonian, Thracian and the Thracesian themes and of the imperial tagmata.Haldon (2004), p. 135
The coordination of all these forces was not easy, but the Byzantine armies, marching from three directions, were able to converge on the same day (2 September) and surround Omar's smaller army at a location called Poson (Πόσων) or Porson (Πόρσων) near the Lalakaon river. The exact location of the river and the battle site have not been identified; most scholars, however, agree that they lay near the river Halys, some southeast of Amisos. With the approach of the Byzantine armies, the only open escape route left to the emir and his men was dominated by a strategically located hill. During the night, both Arabs and Byzantines endeavored to occupy it, but the Byzantines emerged victorious from the ensuing fight. On the next day, 3 September, Omar decided to throw his entire force towards the west, where Petronas was located, in hopes of achieving a breakthrough. The Byzantines, however, stood firm, giving the other two Byzantine wings the time to close in and attack the Arab army's exposed rear and flanks. The rout was complete, as the larger part of the Arab army and Omar himself fell on the field. Casualties also possibly included the Paulician leader Karbeas: although the latter's participation in the battle is uncertain, it is recorded that he died in that year.
Only the emir's son, at the head of a small force, managed to escape the battlefield, fleeing south towards the border area of Charsianon. He was however pursued by Machairas, the kleisourarchēs of Charsianon, and was defeated and captured with many of his men.

Aftermath

thumb|right|250px|The success of the battle of Lalakaon and its follow-up operations enabled the Empire to focus its might against Bulgaria, leading to its successful Christianization. Depiction of the baptism of the Bulgarians from the Manasses Chronicle.
The Byzantines moved quickly to take advantage of their victory: a Byzantine army invaded Arab-held Armenia, and sometime in October–November, defeated and killed the emir 'Ali ibn Yahya.Whittow (1996), p. 311 Within a single campaigning season, the Byzantines had eliminated the three most dangerous opponents on their eastern border. In retrospect, these successes proved decisive, as the battle permanently destroyed the power of Melitene. Lalakaon thus altered the strategic balance in the region, and heralded the beginning of Byzantium's century-long offensive in the East.
The importance of these victories did not go unnoticed by contemporaries: the Byzantines hailed them as revenge for the sack of Amorium 25 years earlier, the victorious generals were granted a triumphal entry into Constantinople, and special celebrations and services were held. Petronas was awarded the high court title of magistros, and Charsianon was raised to a full theme.
The removal of the eastern threat and the rise of the Byzantines' confidence also opened up opportunities in the West, where the Bulgarian ruler Boris had been negotiating with the Pope and Louis the German for a possible conversion of himself and his pagan people to Christianity. This expansion of Rome's ecclesiastic influence up to Constantinople's very doorstep could not be tolerated by the Byzantine government. In 864, the victorious eastern armies were transferred to Europe and invaded Bulgaria, in a demonstration of military might that convinced Boris to accept Byzantine missionaries instead. Boris was baptized, taking the name Michael in honor of the emperor, thus beginning the Christianization of Bulgaria and ensuring that his nation would be part of the Byzantine-influenced, Eastern Orthodox world.