maintenance of its own troops, and the provisioning of the Roman troops stationed there. The Armenian merchants formed the channel for the exchange of goods over the Caucasus with Scythia, over the Caspian Sea with east Asia and China, down the Tigris with Babylonia and India, towards the west with Cappadocia; nothing would have been more natural than to include the politically dependent land in the domain of Roman tribute and customs; yet this step was never taken. The incongruity between the national and the political connections of Armenia forms an essential element in the conflict--prolonged through the whole imperial period--with its eastern neighbour. It was discerned doubtless on the Roman side that annexation beyond the Euphrates was an encroachment on the family-domain of Oriental nationality, and was not any increase proper of power for Rome. But the ground or, if the phrase be preferred, the excuse for the continuance of such encroachment lay in the fact that the subsistence side by side of great states with equal rights was incompatible with the system of Roman policy, we may even say with the policy of antiquity in general. The Roman empire knew as limit, in the strict sense, only the sea or a land-district unarmed. To the weaker but yet warlike commonwealth of the Parthians the Romans always grudged a position of power, and took away from it what these in their turn could not forego; and therefore the relation between Rome and Iran through the whole imperial period was one of perpetual feud, interrupted only by armistices, concerning the left bank of the Euphrates. [Sidenote: The Parthians during the civil wars.]