The Battle of Rhandeia, was a military clash between the Armenian-Parthian and Roman armed forces in the spring of 62 in a place called Rhandeia. The Armenian army was led by Tiridates I the Parthian by Vologases I, and the Roman by Paetus.

The Roman legions pass under the yoke of Armenian spears, which was the most humiliating punishment for a soldier, then flee and leave the territory of the Great Armenian. Two years later, in the year 64, in the same place of the battle, the Treaty of Rhandeia  was signed, by which Tiridates I was declared the Armenian king and founded the Arsacid dynasty of Armenia.

In the early AD 50s, Mithradates, the Roman client-king of Armenia was deposed by a Parthian campaign into the region, and the Parthians installed his brother Tiridates on the throne as their place-man. This was unacceptable to Rome, who felt that their eastern border was being weakened and violated, and so eventually General Corbulo was sent into the region in AD 58 with three legions. After a short year-long campaign, Rome installed Tigranes VI on the throne of Armenia.

But the situation in the east was far from stable and after this same Tigranes of Armenia made an inadvisable probing offensive into Parthia in AD 61, the Parthians under King Vologases counter-attacked against Armenia and laid siege to the city of Tigranocerta, which was garrisoned by both Armenians and Romans. But the city was well-provided for, while the attackers were not, and so a mutual disengagement and withdrawal was negotiated between the two armies.

Paetus nonetheless appeared confident of victory, and followed the Parthian declaration of war and capture of Tigranocerta with his own invasion of Armenia, while Corbulo remained at Syria, further strengthening the fortifications in the Euphrates frontier. Paetus had only two legions with him, IV Scythica and XII Fulminata, and advanced towards Tigranocerta. A few minor forts were taken, but a lack of supplies forced him to withdraw westwards for the winter.

Corbulo in the meantime had been aware of the danger faced by his colleague, and put part of his forces on standby, but he did not march to join Paetus, and some accused him of delaying in order to reap more glory from rescuing him. Nevertheless, when the calls for assistance arrived, he responded quickly and marched forth with half of the Syrian army, carrying many provisions laden on camels. He soon met dispersed men of Paetus' army, and managed to rally them around his force. But before he could arrive to the rescue, Paetus had capitulated: the Parthians, aware that relief was nearing, increasingly harassed the Romans, until Paetus was forced to send a letter to Vologases to seek terms. The subsequent treaty was humiliating: not only would the Romans leave Armenia and surrender all forts they held, but they also agreed to build a bridge over the nearby Arsanias river over which Vologases could pass in triumph, sitting atop an elephant. In addition, the Roman army was liberally plundered by the Armenians, who took even the Romans' weapons and clothes without facing any resistance. Still worse, according to rumors reported by Tacitus, the Romans were made to pass under the yoke, a gesture of ultimate humiliation in Roman eyes.

The two Roman forces met on the banks of the Euphrates near Melitene, amidst scenes of mutual grief; while Corbulo lamented the undoing of his achievements, Paetus tried to convince him to attempt to reverse the situation by invading Armenia. Corbulo, however, refused, claiming that he did not have the authority to do so, and that either way the army was too worn out to be able to campaign effectively. In the end, Paetus retired to Cappadocia and Corbulo to Syria, where he received envoys from Vologases, who demanded that he evacuate his bridgehead over the Euphrates. In turn, Corbulo demanded the Parthian evacuation of Armenia. Vologases agreed to this, and both sides withdrew their forces, leaving Armenia once again masterless but de facto under Parthian control, until a Parthian delegation could travel to Rome.