From, The Travels of Marco Polo, translated by Henry Yule and Henri Cordier, concerning Genghis Khan:
The Lord abides at this Park of his [near Shang-tu in what is now Inner Mongolia], dwelling sometimes in the Marble Palace and sometimes in the Cane Palace for three months of the year, to wit, June, July, and August; preferring this residence because it is by no means hot; in fact it is a very cool place. When the 28th day of August arrives he takes his departure, and the Cane Palace is taken to pieces.
But I must tell you what happens when he goes away from this Palace every year on the 28th of the August.
You must know that the Kaan keeps an immense stud of white horses and mares; in fact more than 10,000 of them, and all pure white without a speck. The milk of these mares is drunk by himself and his family, and by none else, except by those of one great tribe that have also the privilege of drinking it. This privilege was granted them by Chinghis Kaan, on account of a certain victory that they helped him to win long ago. The name of the tribe is HORIAD.
Now when these mares are passing across the country, and any one falls in with them, be he the greatest lord in the land, he must not presume to pass until the mares have gone by; he must either tarry where he is, or go a half-day’s journey round if need so be, so as not to come nigh them; for they are to be treated with the greatest respect. Well, when the Lord sets out from the Park on the 28th of August, as I told you, the milk of all those mares is taken and sprinkled on the ground. And this is done on the injunction of the Idolaters and Idol-priests, who say that it is an excellent thing to sprinkle that milk on the ground every 28th of August, so that the Earth and the Air and the False Gods shall have their share of
it, and the Spirits likewise that inhabit the Air and the Earth. And thus those beings will protect and bless the Kaan and his children and his wives and his folk and his gear, and his cattle and his horses, his corn and all that is his. After this is done, the Emperor is off and away.