Joshua 16:9 - Ellicott's Commentary On The Whole Bible

The separate cities for the children of Ephraim were among the inheritance of the children of Manasseh; and Joshua 17:10-11 : “Manasseh had in Issachar and in Asher, Beth-shean,” &c. This fact would manifestly tend to produce a solidarity among the several tribes, and to prevent disunion by creating common interests. The interest of the stronger tribes would be served by completing the conquest of the territory assigned to the weaker. And the general formation thus produced would resemble that which was known by the name of the testudo, or tortoise, in Roman warfare. When a body of soldiers approached the wall of a town which it was intended to assault, they sometimes held their shields over them, overlapping like scales, each man’s shield partly sheltering his own, and partly his neighbour’s body, so that no missile could penetrate. Thus it may be said not only of Jerusalem, but of all the tribes in the land of their possession, that they were built as a city that is compact together, and at unity in itself: united by joints and bands, so that if one member of the body politic should suffer, all the members must suffer with it. For a further illustration of the same topic, see on the inheritance of Benjamin (Joshua 18:11) and of Simeon (Joshua 19:1).