I think it's actually 5 provinces. They can appear anywhere from the province just north of the Caspian Sea down to Baghdad. Where they appear tends to determine where they go. If they appear in Yerevan they tend to muddle around in the mountains for long periods, if they appear in Baghdad they usually go after the Holy Land, and if they appear north of the mountains they usually wind up going after Russia/Poland.

They appear in waves, too, 3 or 4 waves of troops; I forget which. What I always see is the lead wave moves out and does a few things, then starts backtracking to join up with the second wave. Then the mass moves on for a bit before backtracking to join up with the next wave. This continues until all of them are on the map.

Example from one game: they appeared in the province with the Caspian Sea, just on that little bit of land between the northern edge and the border. The first wave moved west, took Sarkel, and continued on west. They got as far as Kiev before the next wave appeared, at which point they headed back east. After joining the next wave they sacked Sarkel again and returned to Kiev. Before taking Kiev the next wave appeared and they moved east. After joining up and sacking Sarkel yet again they returned to Kiev and this time sacked it. Whether there was a fourth I can't recall, but this stayed the same pattern until they were all on the map. When they were all there, they took Kiev again and settled there, then proceeded to expand and cover the whole northeast region.