Like a good mystery! "At first glance the rectangular island of Por-Bajin looks like a foreboding fortress or prison, with its regular structure and ruined sections. But it is unknown for certain what the rectangular island and its labyrinthine ruins, located in a lake in deepest Siberia, was actually used for when it was built 1,300 years ago. Historians and scientists are divided, but some experts believe the isolated area may have been built to attract people instead imprisoning them, and suggest it was a summer palace, monastery, or an astronomical observatory. The mysterious island, Por-Bajin, was found in the centre of a remote lake high in the mountains of southern Siberia The island has baffled experts for over a hundred years who say it could have been anything from a prison, to a palace or monastry The name Por-Bajin translates as 'clay house' in the Tuvan language, and the island sits between the Sayan and Altai ranges, about 3,800km from Moscow near the Mongolian border. The location was first discovered in 1891, and the purpose of island has still not been explained over a century later." http://www.dailymail.co.uk/travel/travel_news/article-3028656/The-ancient-fortress-historians-Putin-baffled-knows-spectacular-1-300-year-old-Siberian-island-fort-built-abandoned.html#ixzz3WoeuZybR And here's an archaeological viewpoint- http://archive.archaeology.org/1011/etc/letter.html
Fascinating! If the Uighurs were chased out of there shortly after building, it might have been looted of artifacts for quite some time by the local tribes. Ceramics, metal objects and so forth would have been quite precious. The burning of the site might have occurred much later.
Archeologist consider things artifacts which then and now would be considered garbage. A campfires remains or a latarine can be quite useful in reconstructing the lives of those who occupied an area. It sounds like even that is missing for the most part. If it was some sort of ceremonial structure it might make sense that they kept it clean and even if it was being abandoned to have scoured it a final time. The fact that so much of the sturcture is left suggest looting was limited as well. I would expect the stone for instance to have been valuable to the locals as well. Of course if it were still considered to be a "place of power" which the one article indicated that might explain the lack of looting but I would think it would explain it on all levels. Certainly a lot of questions and not a whole lot of answers at this point.
In fairness, it's on an island in a lake 7500 feet up the mountains, so not exactly handy for a quick bit of looting.
So why is it so "clean"? The number of artifacts found so far is extremely small and my impression is that they have been working there for a while. They didn't go into a lot of detail on it but I'm assuming they don't have much in the way of even food remains or they would have mentioned it.
The very remoteness makes anything lying around that much more precious to any wandering goat herder (or whatever they herd in those parts). It's just that if it ended due to an attack then one would expect to find lots of broken bits, bones, etc. If they were just pressured out and the site became untenable, they might carry what they could and the rest would be left to be taken over a number of years by anyone passing through. A ceramic bowl, some bits of iron, stuff like that would be real treasure to somebody in such a remote area. You might ride there from miles away just to look for such things. I guess I'm just making the point that just because there are signs of a fire, doesn't necessarily mean that the fire was concurrent with the end of habitation. It might have happened much later for any number of reasons; "This is an old Uighur place, different tribe, different religion, why don't we burn it down since we're passing through..."
I agree with Kodiak; the Romans were known to actually dismantle forts when they abandoned them, maybe the people who built this took everything they could carry, but didn't have time to torch the place. We'll probably never know.
If it fell to a hostile power I would expect more artifacts and remains to have been found. But it sounds like they did more than just cary off what they could it sounds like they spent some effort cleaning it up before they left (possibly the surrounding lake has a good selection of the artifacts and given the temp they may be in pretty decent shape. *** edit for *** A thought just came to me. I think they mentioned that there weren't any obvious heat sources for the various buildings. What if it was a ceremonial site that was only used in the summer? As such cleaning it up at the end of the use period might make a lot of sense. If at some point they couldn't get back to it then it would be as mentioned and even less a target for looters. The stone structure aside but if the locals weren't living close I'm not sure it would make sense to loot the stone.