The upper fort is a quadrangular building on the summit, with only one approach, and was deemed impregnable by the Mysore princes.
At dawn the mistake was realized, but the quick-following enemy were already in possession of Pria Fora, which is almost impregnable from the south.
The town, which had grown up under the shadow of the almost impregnable castle, was first incorporated by Henry I.
After an unsuccessful attempt to come to terms, he drove the Macedonians from the valley of the Aous by skilfully turning an impregnable position.
From Arkona Absalon proceeded by sea to Garz, in south Rugen, the political capital of the Wends, and an all but impregnable stronghold.
Moreover, the site constituted a natural citadel, difficult to approach or to invest, and an almost impregnable refuge in the hour of defeat, within which broken forces might rally to retrieve disaster.
Benedict XIII., who had on his part tried to call together a council at Perpignan, was by this time recognized hardly anywhere but in his native land, in Scotland, and in the estates of the countship of Armagnac. He remained none the less full of energy and of illusions, repulsed the overtures of Sigismund, king of the Romans, who had come to Perpignan to persuade him to abdicate, and, abandoned by nearly all his adherents, he took refuge in the impregnable castle of Peniscola, on a rock dominating the Mediterranean (1415).
Abandoned by almost all his adherents Benedict found refuge in the castle of Peniscola on an impregnable rock overlooking the Mediterranean, and remained intractable.
Captain Popham, with a small detachment, stormed the rock fortress of Gwalior, then deemed impregnable and the key of central India; and by this feat held in check Sindhia, the most formidable of the Mahratta chiefs.
Belisarius pursued his diminished army northwards, shut him up in Ravenna, and ultimately received the surrender of that impregnable city.