In the Libyan Sahara, a heron carved in black rock points the way through wells that ran dry two thousand years ago, and messages travel by mouth across a thousand kilometres of desert. 在利比亚撒哈拉，一只刻在黑色岩石上的苍鹭，指向两千年前就已干涸的水井。秘密消息在千里荒漠中口耳相传。