strong fortress
この堅城は百年間一度も落ちなかった。
This strong fortress never fell in a hundred years.
堅城を築くため巨石が積み上げられた。
Huge stones were piled up to build the strong fortress.
名将が守る堅城に敵は手も足も出ない。
The enemy is helpless against the fortress defended by a great general.