John Gill Commentary Judges 11:19

"And Israel sent messengers unto Sihon king of the Amorites, the king of Heshbon; and Israel said unto him, Let us pass, we pray thee, through thy land unto my place." — Judges 11:19 (ASV)

And Israel sent messengers to Sihon king of the Amorites,
the king of Heshbon
Which was his royal city, where he had his palace and kept his court. It is therefore particularly mentioned, and the rather because he had taken it from the Moabites, and was part of that land now in dispute; and this Sihon was not only in possession of, when Israel sent messengers to him, but it was his royal seat, the metropolis of his kingdom, and he was called king of it:

and Israel said to him, let us pass, we pray you, through your land
to my place ;
the land of Canaan, prepared and reserved for them when the Most High divided to the nations their inheritance, promised by the Lord to their ancestors and to them, and given to them, who is sovereign Lord of all. All that Israel desired of Sihon was only a passage through his land to that, promising the same as to the king of Edom; see the history of it in (Numbers 21:21–35) .