From Mao Zedong's 1956 ci-poem 《
水调歌头·
游泳》, written after swimming across the Yangtze and commemorating the then-under-construction Wuhan Yangtze Bridge:
一桥飞架南北,
天堑变通途 — 'One bridge flies across north and south; the heavenly moat becomes a thoroughfare.'
天堑 originally referred specifically to the Yangtze as a strategic barrier.