Leviticus 25:30-31
25:30 If it is not redeemed before the full calendar year is ended, the house in the walled city will belong without reclaim to the one who bought it throughout his generations; it will not revert in the jubilee.
25:31 The houses of villages, however, which have no wall surrounding them must be considered as the field of the land; they will have the right of redemption and must revert in the jubilee.