Russian fortificationsin occupied Ukrainian territoryBy region (from south to north)CrimeaKhersonZaporizhzhiaLuhanskKharkivDonetskRUSSIATerritoryoccupiedby RussiaKyivUKRAINEKharkivZaporizhzhiaKhersonBlack Sea200 Km1. According to John Helin, a Finnish historian and military analyst, Russian forces have also fortified municipalities to turn them into strongholds behind the lines, which Ukrainian forces will have to take one by one to avoid leaving enemy units in their own rearguard. Well-trained and shrewdly directed attackers with numerical superiority,” the Columbia professor notes, “can achieve progress on the ground, but slowly and at great cost