“Another great and terrible thing I saw. For, as I went through a certain valley which lieth by the River of Delights (_flumen deliciarum_) I saw therein many dead corpses lying. And I heard also therein sundry kinds of music, but chiefly nakers, which were marvellously played upon. And so great was the noise thereof that very great fear came upon me. Now, this valley is seven or eight miles long; and if any unbeliever enter therein, he quitteth it never again, but perisheth incontinently. Yet I hesitated not to go in that I might see once for all what the matter was. And when I had gone in I saw there, as I have said, such numbers of corpses as no one without seeing it could deem credible. And at one side of the valley, in the very rock, I beheld as it were the face of a man very great and terrible, so very terrible indeed that for my exceeding great fear my spirit seemed to die in me. Wherefore I made the sign of the Cross, and began continually to repeat _Verbum caro factum_, but I dared not at all come nigh that face, but kept at seven or eight paces from it. And so I came at length to the other end of the valley, and there I ascended a hill of sand and looked around me.” Narrated as it is of no specified place and of no one year of his journey, it may stand, and perhaps it was meant to stand, for a common experience of China in the period of Mongol decadence. Whether he left the country by the gorges of the Yang-tsi and the Yun-nan route, or along the upper basin of the Hoang-ho by the more usual northern route to the desert of Gobi, his vision of a Valley of Corpses is equally significant. The Theory of the Plague-Virus.