Deuteronomy 19:9

if thou shalt keep all these commandments to do them, which I command thee this day, to love the Lord, thy God, and to walk ever in His ways, this being the condition that must be fulfilled before the great territory would be given to the Israelites, then shalt thou add three cities more for thee, beside these three, thus making a total of nine in the entire region occupied by the Israelites. As a matter of fact, this condition was never fulfilled by the people, and therefore the number of the cities of refuge never exceeded six. Even at the time of David and Solomon, whose power extended from the brook of Egypt and the Elanitic Gulf to the Euphrates, the children of Israel were not actually occupying all this country, many of the conquered nations being merely tributary, vassals, who retained their form of government and their national identity;