Exploiting Parthian instability, Rhadamistus of Iberiainvaded Armenia in 50 AD and executed the king, even though both were Roman allies. Although Rome accepted Rhadamistus’ power grab, Parthia—by now under the firm rule of Vologases I (51–78)—did not and in 52 AD marched into Armenia with their own claimant, Vologases’ brother Tiridates. However, the expedition was crippled by winter and disease, forcing Tiridates to withdraw the following year.
Both persuaded by and fearing his manipulative son Rhadamistus, the elderly King Pharasmanes I of Iberia declared war on his brother, King Mithridates of Armenia, in 50 AD, even though both kings were clients of the Roman Empire. Invading with a strong army, Rhadamistus besieged Mithridates at Gorneas (Garni) until the king was betrayed by his Roman garrison and executed by Rhadamistus while negotiating peace. Rhadamistus then proclaimed himself King of Armenia and was recognized as such by Rome.in wikipedia
Concerned by the usurpation of the Armenian throne by the Iberian prince Rhadamistus, Shah Vologases I of Parthia named his younger brother Tiridates as King of Armenia and sent him with an army to depose Rhadamistus. In 52 AD Tiridates invaded, capturing the Armenian capitals of Tigranocerta and Artaxata and dispersing the Iberian forces effortlessly. However, in the bitter winter that followed an epidemic ravaged the Parthian troops, forcing them to withdraw and allowing Rhadamistus to regain control of the country.in wikipedia
