Its history is divided into the successive reigns of three royal dynasties: Orontid (331 BC–200 BC), Artaxiad (189 BC–12 AD), and Arsacid (52–428).

During the Roman Republic's eastern expansion, the Kingdom of Armenia, under Tigranes the Great, reached its peak, from 83 to 69 BC, after it reincorporated Sophene and conquered the remaining territories of the falling Seleucid Empire, effectively ending its existence and raising Armenia into an empire for a brief period, until it was itself conquered by Rome in 69 BC.

Throughout most of its history during this period, Armenia was heavily contested between Rome and Parthia, and the Armenian nobility was divided among pro-Roman, pro-Parthian or neutral factions.

Prior to the 9th century BC, the geographic region known as the Armenian Highlands was inhabited by Proto-Armenian and other tribes which did not yet constitute a unitary state or nation.

Both kingdoms fell to Iranian invaders from the east (the Medes,[12] followed by the Achaemenid Persians) in the 6th century BC.

Orontes III also defeated the Thessalian commander Menon, who wanted to capture Sper's gold mines.

Artaxias seized Yervandashat, united the Armenian Highlands at the expense of neighboring tribes and founded the new royal capital of Artaxata near the Araxes River.

[17] The new city was laid on a strategic position at the juncture of trade routes that connected the Ancient Greek world with Bactria, India and the Black Sea which permitted the Armenians to prosper.

In 83 BC, at the invitation of one of the factions in the interminable civil wars, he entered Syria, and soon established himself as ruler of Syria—putting the Seleucid Empire virtually at an end—and ruled peacefully for 17 years.

[18] During the zenith of his rule, Tigranes the Great extended Armenia's territory outside of the Armenian Highland over parts of the Caucasus and the area that is now south-eastern Turkey, Iran, Syria and Lebanon, becoming one of the most powerful states in the Roman East.

[20] In 20 BC, Augustus negotiated a truce with the Parthians, making Armenia a buffer zone between the two major powers.

Subsequently, Armenia was often a focus of contention between Rome and Parthia, with both major powers supporting opposing sovereigns and usurpers.

After gaining Armenia in 60, then losing it in 62, the Romans sent the Legio XV Apollinaris from Pannonia to Gnaeus Domitius Corbulo, legatus of Syria.

An agreement was reached at the Treaty of Rhandeia in 63, according to which members of the Parthian Arsacid dynasty would rule Armenia as client kings of Rome.

[22] Another campaign was led by Emperor Lucius Verus in 162–165, after Vologases IV of Parthia had invaded Armenia and installed his chief general on its throne.

After the fall of the Arsacid dynasty in Persia, the succeeding Sassanid Empire aspired to reestablish Persian control.

According to the author of Judith, his army included chariots and 12,000 cavalrymen, most likely heavy cavalry or cataphracts, a unit also commonly used by Seleucids and Parthians.

These followers consisted of camels, donkeys, and mules used for baggage, sheep, cattle, and goats for food, said to be stocked in abundance for each man, and hoards of gold and silver.

[28] Note that the numbers given by Israelite historians of the time were probably exaggerated, considering the fact that the Hasmonean Jews lost the war against Tigranes.

The Romans admired and respected the bravery and the warrior spirit of the Armenian Cavalry – the core of Tigran's Army.

In medieval times, the cavalry were collected from nobles (usually the youngest sons of Armenian lords), and were known as Ayrudzi, or "horsemen."

It is most likely that the Armenian First Legion was formed in the 2nd or 3rd century AD, in the western part of the Kingdom, with the mission to protect the lands of Armenia from intrusion.

The Armenian Second legion is mentioned in the year 360 AD as a part of the garrison of Bezabda (anciently called Phoencia) in upper Tigris.

The pre-Christian Armenian pantheon included: During the 1st century AD, Christianity spread through Armenia due to (according to legend) the efforts of the apostles Bartholomew and Thaddeus.

In 189 BC when Artashes I's reign began, many neighboring countries (Media, Caucasian Iberia, Seleucid Empire) exploiting the weakened state of the kingdom, conquered its remote regions.

At its peak, under Tigranes the Great, it incorporated, besides Armenia Major, Iberia, Albania, Cappadocia, Cilicia,[44] Armenian Mesopotamia, Osroene, Adiabene, Syria, Assyria, Commagene, Sophene,[45] Judea and Atropatene.