Exodus 21:13 is the original law God gave Moses about unintentional killers fleeing to a designated place — the basis for this command.

Exodus 21:14 contrasts intentional murder with no refuge — highlighting why cities of refuge are only for accidental killing.

Numbers 35:6 also commands cities of refuge for the Levites — the same institution Joshua is now implementing.

Numbers 35:11-14 provides the specific plan for six cities of refuge — the direct basis for Joshua’s command here.

Numbers 35:15-24 gives the original law for cities of refuge which Joshua 20:2 is now implementing — a direct legislative link.

Deuteronomy 4:41-43 records Moses already setting aside three refuge cities east of the Jordan — Joshua now continues on the west side.

Deuteronomy 19:2-13 contains the full law of cities of refuge that Joshua 20:2 is now enacting.

Hebrews 6:18 directly echoes the cities-of-refuge imagery, describing how we flee to Christ for safety as the manslayer fled to the city.