The French Sinologist, Paul Pelliot, said, "Until now no trace can be found to show that the Chinese had already opened up the communication between Yunnan and Hanoi before the T'ang dynasty." In fact, such route had been developed as far back as in the Han and Chin periods. At that time, people who travelled by way of that route were quite numerous. There is a detailed description of Ma Yüan's 馬援 plan to attack Yunnan by way of the watercourse from Hanoi in the great geographical account, Shui-ching chu 水經注. That watercourse was known as the Yeh-yü River 葉榆水, i.e., the present P'an-Iung Chiang 盤龍江, and not the present Fleuve Rouge. As there have been confusing interpretations of the exact location of that watercourse, an appendix to this article is written in an attempt to clarify the confusion.