John Gill Commentary Joshua 13:10

"and all the cities of Sihon king of the Amorites, who reigned in Heshbon, unto the border of the children of Ammon;" — Joshua 13:10 (ASV)

And all the cities of Sihon king of the Amorites, which
reigned in Heshbon
A city he took from the Moabites, and made it his royal seat, (Numbers 21:26):

unto the border of the children of Ammon;
which was the river Jabbok, (Deuteronomy 3:16).