as firm (/hard/steady/steadfast/solid) as a rock; monolithic;rock-firm ❍ 我国各族人民之间的团结～。The solidarity between the nationalities of our country is as firm as a rock.
坚如磐石jiān rú pán shí
磐石：大而厚的石头。比喻十分坚固，不可动摇。solid as a rock, rock-firm, as firm as a rock, granite