Incapable of being conquered, overrun, or subjugated
Grabusa, long regarded as an impregnable fortress, was surrendered in 1692, Suda (where the flags of Turkey and the four protecting powers are now hoisted) and Spinalonga in 1715.
Impregnable Malta surrenders without a shot; his most reckless schemes are crowned with success.
3 Not until the district was cleared could Jerusalem be taken, and the capture of the almost impregnable Jebusite fortress furnished a centre for future action.
The upper fort is a quadrangular building on the summit, with only one approach, and was deemed impregnable by the Mysore princes.
Abandoned by almost all his adherents Benedict found refuge in the castle of Peniscola on an impregnable rock overlooking the Mediterranean, and remained intractable.