The four tribes of the Wagon Peoples war amongst each other more or less continuously; but once every ten years they come together during a season called The Omen Year. The Omen Year actually spans parts of two different regular years, which are calculated by the Wagon Peoples from one Season of Snows to the next Season of Snows. The Omen Year lasts several months, and is comprised of three phases related to the seasonal migrations of the bosk.
The first phase is known as the Passing of Turia, and takes place during the autumn. The second phase is called the Wintering, and takes place when the tribe is camped to the north of Turia and south of the Cartius River. (The equator, in the southern hemisphere, is, of course, to the north; thus it is in the north that the Wagon Peoples are most likely to find grass for the bosk during the cold winter months.)
The third and final phase of the Omen Year is called the Return to Turia, which takes place in the spring, or Season of Little Grass. It is at this time that the omens are read by hundreds of haruspexes, in verr livers and bosk blood, to determine whether the time is right for the choosing of an Ubar San, or High Ubar , to rule over all the four tribes of the Wagon Peoples, thus bringing them together under one fearsome war standard.
The omens had not been favourable for the choosing of an Ubar San for over a hundred years, at the time when Kamchak of the Tuchuks became Ubar San with Aphris of Turia at his side as Ubara Sana of the Wagon Peoples. The joining together of the Wagon Peoples presented a terrible threat to all of the cities of the north. United, they would be unstoppable in their march northwards and eastwards. It was said that once, a thousand years ago, they had carried devastation all the way to Ko-Ro-Ba itself.