Joshua, or whoever else is the historian before he comes to sum up the new conquests Israel had made, in these verses receives their former conquests in Moses's time, under whom they became masters of the great and potent kingdoms of Sihon and Og. Note, Fresh mercies must not drown the remembrance of former mercies, nor must the glory of the present instruments of good to the church be suffered to eclipse and diminish the just honour of those who have gone before them, and who were the blessings and ornaments of their day. Joshua's services and achievements are confessedly great, but let not those under Moses be overlooked and forgotten, since God was the same who wrought both, and both put together proclaim him the Alpha and Omega of Israel's great salvation. Here is, 1. A description of this conquered country, the measure and bounds of it in general (Jos 12:1): From the river Arnon in the south, to Mount Hermon in the north. In particular, here is a description of the kingdom of Sihon (Jos 12:2, Jos 12:3), and that of Og, Jos 12:4, Jos 12:5. Moses had described this country very particularly (Deu 2:36; Deu 3:4, etc.), and this description here agrees with his. King Og is said to dwell at Ashtaroth and Edrei (Jos 12:4), probably because they were both his royal cities; he had palaces in both, and resided sometimes in one and sometimes in the other; one perhaps was his summer seat and the other his winter seat. But Israel took both from him, and made one grave to serve him that could not be content with one palace. 2. The distribution of this country. Moses assigned it to the two tribes and a half, at their request, and divided it among them (Jos 12:6), of which we had the story at large, Num. 32. The dividing of it when it was conquered by Moses is here mentioned as an example to Joshua what he must do now that he had conquered the country on this side Jordan. Moses, in his time, gave to one part of Israel a very rich and fruitful country, but it was on the outside of Jordan; but Joshua gave to all Israel the holy land, the mountain of God's sanctuary, within Jordan: so the law conferred upon some few of God's spiritual Israel external temporal blessings, which were earnests of good things to come; but our Lord Jesus, the true Joshua, has provided for all the children of promise spiritual blessings - the privileges of the sanctuary, and the heavenly Canaan. The triumphs and grants of the law were glorious, but those of the gospel far exceed in glory.

From the river Arnon unto Mount Hermon - Arnon was the boundary of all the southern coast of the land occupied by the Israelites beyond Jordan; and the mountains of Hermon were the boundaries on the north. Arnon takes its rise in the mountains of Gilead, and having run a long way from north to south falls into the Dead Sea, near the same place into which Jordan discharges itself.
And all the plain on the east - All the land from the plains of Moab to Mount Hermon.

Now these are the kings of the land which the children of Israel smote,.... In the days of Moses, as Jarchi remarks, and as it clearly appears from what follows:

and possessed, their land on the other side Jordan toward the rising of the sun; on the east of the land of Canaan:

from the river Arnon unto the mount Hermon, and all the plain on the east; Arnon was the border of Moab between them and the Amorites, Num 21:13; and from hence to Hermon, a mountain adjoining to Lebanon, lay the country of the two kings of the Amorites after mentioned, Deu 3:8; and the plain on the east were the plains of Moab, which lay to the east of Jordan.