Archaeologists in southwest Russia have unearthed a trove of medieval silver at a site where treasure was often hidden from an invading Mongol army in the 13th century — but oddly it seems to have been buried there at least 100 years before the Mongols swept through.The trove of silver pendants, bracelets, rings, and ingots was found during excavations earlier this year near the site of Old Ryazan, the fortified capital of a Rus principate that was besieged and sacked by Mongols in 1237.The Mongol attack was particularly bloodthirsty; historical accounts report that the invaders left no one alive in...