There were12towns in which the Merarites resided: four in Zebulun ( Joshua 21:34-35), four in Reuben ( Joshua 21:36-37), and four in Gad ( Joshua 21:38-39). [source][source][source]
In all, the Levites received48 cities with their surrounding pasturelands, including the six cities of refuge ( Joshua 21:41-42). God provided so that the Levites, whose responsibilities included the teaching and counseling of the other Israelites in the Law, were not far from anyone in Israel. They were to provide a positive spiritual influence on the whole nation. [1][source]
"For Christians, the allotment of Levitical towns from each tribe illustrates the principle of returning to God a portion of what has been given to them. These gifts are then used to support others in need and to encourage the proclamation of the faith (cf. Acts 2:44-47; Romans 15:26-27; Philippians 4:10-18)." [2][source]
"Take special care of the poor clergy! This is the theme of the complex formed by Numbers 35 and Joshua 21 , along with the relevant Deuteronomic laws." [3][source]