zhè / zuò / biān / ài / céng / jīng / shì / shāng / lǚ / jìn / rù / nèi / dì / de / bì / jīng / zhī / lù

这座边隘曾经是商旅进入内地的必经之路。

This frontier pass was once the only route for merchants and travelers entering the interior.