Another element of a fortress was the citadel. The castle became a fortress, then a mansion. It may be a castle, fortress, or fortified center. It was a fortified town, had walls, and a separate fortress or alcazar. Other fortifications include the Kazarma fortress at Sitia. The well-defended fortress of Taillebourg seemed impregnable. Marlborough acquiesced and resolved upon the siege of Vauban's great fortress, Lille. Castrum occupied part of today's Belgrade Fortress. Warriors lock him away in an abandoned fortress. The two live in the ancient library fortress of Candlekeep. It is believed that it is the remnants of the Acra fortress. The Ottoman Empire began the war with 61,250 men in the fortress. He aimed to avoid new, complex city combat in Vyborg, an old military fortress. Out of 6,500 defenders of Brest Fortress, 6,000 Soviet troops capitulated. The village was prepared for the attack, evidenced by its fortress and system of tunnels.