After the Roman Republic completed its brief conquest of what is now Georgia in 66 BC, the area became a primary objective of what would eventually turn out to be over 700 years of protracted Irano–Roman geo-political rivalry and warfare. From the first centuries A.D, the cult of Mithras, pagan beliefs, and Zoroastrianism were commonly practised in Georgia. In 337 AD King Mirian III declared Christianity as the state religion, giving a great stimulus to the development of literature, arts, and ultimately playing a key role in the formation of the unified Georgian nation, The acceptance led to the slow but sure decline of Zoroastrianism, which until the 5th century AD, appeared to have become something like a second established religion in Iberia (eastern Georgia), and was widely practised there.