Joshua 21:19

All the cities of the children of Aaron, the priests, were thirteen cities with their suburbs.

The thirteen cities were part of the larger provision for Levi, which received no single territory of its own but forty-eight cities scattered throughout Israel. Within that scattering, thirteen cities were assigned to the priestly descendants of Aaron. This dispersion throughout Israel fulfilled Jacob's prophecy concerning Levi. When the other tribes apostatized, Levi remained faithful to God and was therefore given service at the sanctuary. By that appointment the curse of scattering was turned into a blessing.