Impregnable

#137
Impregnable
- Impossible to capture or enter by force.
- Strong enough to resist or withstand attack.

The old intra-mural city of Manila is surrounded by a parapeted wall which, at the time it was built, was considered to be one of the most impregnable fortifications in the world.
Image Credits : John Tewell 

Usage:
- Apple Inc Claims Its New iPhones Are Impregnable.
- Each clan added such wonderful innovations to the fort’s defences that Daulatabad was considered virtually impregnable.
- Cook’s fortitude and defence looked impregnable.