Exegetical and Hermeneutical Commentary of Joshua 21:33
All the cities of the Gershonites according to their families [were] thirteen cities with their suburbs.
All the cities of the Gershonites, according to their families,…. Which were divided among them, according to the number of their families:
[were] thirteen cities with their suburbs; two out of the half tribe of Manasseh beyond Jordan, four out of Issachar, four out of Asher, and three out of Naphtali.
Fuente: John Gill’s Exposition of the Entire Bible
‘ All the cities of the Gershonites, according to their families, were thirteen cities with their suburbs.’
So the Gershonites acted as Levites in the northern territories, Asher, Naphtali, Issachar and Manasseh in Transjordan.