impassable; impervious;insurmountable; insuperable; not be overstepped;unbridgeable
? 到了十九世紀中葉，西方突破了中國孤立的墻壁，那在以前是～的。(《毛澤東選集》1401) Then in the middle of the nineteenth century the heretofore impervious wall of Chinese isolation was breached by the West.
不可逾越
impassable;indespensible;insurmountable
～的鴻溝impassable chasm/～的階段indespensible stage/～的障礙insurmountable obstacle
不可逾越bù kě yú yuè
逾：越過。不能越過。impassable, insuperable, impervious, insurmountable