The prison , initially designed for a population in the hundreds , was an old brick building surrounded by one wall 15 feet high , another of 30 feet , a 10 foot high wall topped with electrified wire , followed by a wall of barbed wire . The prison , initially designed for a population in the hundreds , was an old brick building enclosed by one wall 15 feet high , another of 30 feet , a 10 foot high wall topped with electrified wire , followed by a wall of barbed wire .