Russia's most mysterious archaeological site takes up a vast majority of a small island in the center of a remote lake high in the mountains of southern Siberia. Por-Bajin, the fortress, was supposedly built by the Uighurs, and there were excavations conducted on the site during the 1950s and the 1960. But now Irina Arzhantseva of the Russian Academy of Sciences is digging here for the Por-Bajin Cultural Foundation to find out when the complex was truly built and for what purpose. The few artifacts discovered at the site seem to be dated back to the mid-eighth century A.D. That was the time period of the Uighurs, who might have built the site on an island for defense from forces of warriors on horseback. Or, perhaps the island was the site of a palace or a memorial for a ruler. Por-Bajin's unique layout, more complex than that of other Uighur fortresses of the period, has led some scholars to suggest that it might have had a ritual role. The Uighurs eventually adopted Manichaeism so Por-Bajin was probably built by the son of a Uighur and a Chinese princess who married, Bö-gü, who converted to Manichaeism. The truth is that even now, after archaeologists have excavated one-third of the site to exacting standards, Por-Bajin remains a mystery, but with multiple theories.