After the death of Emperor Theodosius II on 28 July 450, Marcian was made a candidate for the throne by Aspar, who held much influence because of his military power.

Zeno, a military leader whose influence was similar to Aspar's, may have been involved in these negotiations, as he was given the high-ranking court title of patrician upon Marcian's accession.

This action, accompanied by the famine and plague that broke out in northern Italy, allowed the Western Roman Empire to bribe Attila into retreating from the Italian peninsula.

After Attila's death in 453, Marcian took advantage of the resulting fragmentation of the Hunnic confederation by settling Germanic tribes within Roman lands as foederati ("federates" providing military service in exchange for benefits).

Evagrius Scholasticus, Procopius and later authors give a likely false account in which Marcian, while in captivity, met the Vandal king Gaiseric, who predicted he would later become emperor.

To the north, the Huns, who had customarily attacked the empire whenever its armies were preoccupied, withdrawing as those forces returned, sent ambassadors to Theodosius in 431, demanding tribute.

In the spring of 440, 1,100 ships set sail from Constantinople for Africa;[9] sending away so many of the Eastern Roman forces was a huge gamble on Theodosius' part.

He was betting the fortified cities along the Danube could delay the Huns long enough for the invasion force to gain a secure foothold in Africa, allowing troops to be withdrawn back to the northern frontier.

[10] After Theodosius II died unexpectedly in a riding accident on 28 July 450, the Eastern Roman Empire faced its first succession crisis in 60 years.

"[19] Lee states that Marcian "can appear as a stronger figure than many other fifth-century incumbents of the imperial office", but notes that "Flavius Zeno and Pulcheria had both been opponents of Chrysaphius, so the changes may be more a reflection of their influence.

[6] Flavius Aetius, who was the supreme commander of the Western Roman army as Comes et Magister Utriusque Militiae, organized a defense and called upon the Visigoths, Franks, Burgundians, Alans, Saxons, Celtic Armoricans, and other tribal groups numbering about 60,000 to aid him.

[21] Attila sacked Metz and attempted a siege of Orléans, before meeting Aetius' forces at the Battle of the Catalaunian Plains, in northeast Gaul.

[23] Despite the plunder he now had from capturing Aquileia, Milan, and other cities, Attila was quickly placed in a precarious situation, because of the actions of both Eastern and Western Rome.

As well, Attila's homeland was threatened by the Eastern Empire which, despite the punitive raids he ordered, took the offensive against the Great Hungarian Plain in mid-452, attacking across the Danube and inflicting a defeat upon the Huns.

Ardaric, alongside the Ostrogoth leaders Theodemir, Valamir and Videmir, decisively defeated Attila's oldest son, Ellac, at the Battle of Nedao in 455, where he was slain.

[26] In the wake of the reduced power of the Hunnic Empire, Marcian accepted the Ostrogoths, who had established themselves in Pannonia Prima and Valeria—nominally two Western Roman provinces—as foederati.

Marcian's successors would grant the status of foederati to multiple peoples and ceding them lands in the recovered European provinces: the Rugians in eastern Thrace, Sciri in Lower Moesia and Scythia, Gepids in Dacia.

[2][27] With the Hunnic empire's diminished might after the death of Attila, Marcian enjoyed a relatively peaceful reign, although he won some small campaigns against the Saracens in Syria and against the Blemmyes in Egypt.

[41] The anti-Miaphysite resolutions of the council led to a large increase in civil disruption in the eastern provinces of Syria and Egypt, where the majority of the population was Miaphysitic.

[49] Marcian removed the financial responsibilities of the consuls and praetors, held since the time of the Roman Republic, to fund public sports and games or give wealth to the citizens of Constantinople, respectively.

[49] By the time of his death, Marcian's shrewd cutting of expenditures and his avoidance of large-scale wars left the Eastern Roman treasury with a surplus of 100,000 pounds (45,000 kg) of gold.

[2][15] It is unknown if Aspar and Ardabur influenced Marcian's policies directly, but if so, they were extremely careful to avoid upsetting the ruling elites of Constantinople.

[70] When Marcian granted part of Pannonia to the Ostrogoths, and the Tisza region to the Gepids, he was accused of encroaching upon the border of Western Roman land.

Because of Euphemius' influence over foreign policy, some historians, such as Edward Arthur Thompson, have suggested that this account was a part of official imperial propaganda, which was generated to excuse Marcian's lack of retribution towards the Vandals, and quell any discontent.

[73] Marcian made several diplomatic attempts to have the prisoners returned, before finally beginning to plan an invasion of the Vandal's territory shortly before his death.

[74] The historian Frank Clover has suggested that this sudden reversal of policy was caused by the marriage of Eudocia to Huneric, the son of Gaiseric, which led to such pressure from Eastern Roman elites that Marcian was forced to begin preparations for war to ensure the return of the hostages.

Most scholars take a more conservative stance on it; Ernst Stein suggests that it is merely a reflection of West Roman propaganda, whereas Norman Baynes believes it indicates that Marcian was cordial to Avitus, neither hostile nor friendly.

[2][82][83] He was buried in the Church of the Holy Apostles, in Constantinople, next to his wife Pulcheria,[2][82] in a porphyry sarcophagus that was described in the 10th century by Constantine VII Porphyrogenitus in the De Ceremoniis.

A later source claims that the Eastern Roman Senate offered to elect Aspar himself, but he declined, with the cryptic comment: "I fear that a tradition in ruling might be initiated through me".

Not only had he been fortunate enough to have Pulcheria to legitimize his rule, but for much of it the two greatest external threats to Rome, the Sassanian Empire and the Huns, were absorbed with their own internal problems.