Genesis 25:16

These [are] the sons of Ishmael
The twelve before mentioned, ( Genesis 25:13-15 ) : these [are] their names, by their towns and by their castles;
their towns and their castles being called after their names, some of which we are able to trace at this distance, as the above notes show: twelve princes according to their nations;
these were princes, or heads of tribes, and there were twelve of them, and continued so, see ( Genesis 17:20 ) ; where is the prophecy, and here an accomplishment of it.