cities of refuge
Towns which, according to Jewish law, enjoyed the right of asylum, and to which anyone who had unintentionally killed another might flee and be protected from the "avenger of blood."
In order to justify his claim to immunity the fugitive had to prove to the authorities that his deed was unpremeditated, and he became virtually a prisoner within the limits of the city to which he fled.
The biblical cities of refuge were Cedes, Sichem, Hebron, Bosor, Ramoth in Galaad, and Gaulon in Basan (Josue 20).
New Catholic Dictionary