The Bible seldom mentions Bezer, but it explains the town's purpose as a refuge in Deuteronomy 4:43, Joshua 20:8, Joshua 21:36, 1 Chronicles 6:78 and 1 Chronicles 7:37. It also fulfilled one of the three promises to Abraham that for a great nation, land, and that his seed would stay in line and that it would not stop.
Cities of refuge were necessary because the next of kin of a manslaughter victim had a right and obligation under the Law of Moses to seek compensation - in kind - for blood shed by the perpetrator.
Therefore, anyone accused of homicide would flee to a city of refuge, to be protected from the victim's family. Once he was there, a manslaughterer was prohibited from leaving until the high priest had died or until his own death, even if the victim's family had forgiven them. Although these cities of refuge were never meant to be a harboring place for murderers, this is what they became.
The Reubenites revolted against Moses and the Law. [There is no verification of this in the Bible]. By then, the Reubenites numbered about forty-eight thousand people; enough to field its own army, if needed.