By the terms of the agreement made after Ipsus, Seleucus was recognized as monarch of all the Greek conquests in Asia, with the sole exceptions of Lower Syria and Asia Minor.
The monarchy thus established extended from the Holy Land and the Mediterranean on the west, to the Indus valley and the Bolor mountain-chain upon the east, and from the Caspian and Jaxartes towards the north, to the Persian Gulf and Indian Ocean towards the south.

It comprised Upper Syria, Mesopotamia, parts of Cappadocia and Phrygia, Armenia, Assyria, Media, Babylonia, Susiana, Persia, Carmania, Sagartia, Hyrcania, Parthia, Bactria, Sogdiana, Aria, Zarangia, Arachosia, Sacastana, Gedrosia, and probably some part of India.

Its entire area could not have been much less than 1,200,000 square miles.

Of these, some 300,000 or 400,000 may have been desert; but the remainder was generally fertile, and comprised within its limits some of the very most productive regions in the whole world.

The Mesopotamian lowland, the Orontes valley, the tract between the Caspian and the mountains, the regions about Merv and Balkh, were among the richest in Asia, and produced grain and fruits in incredible abundance.