Policemen patrol the site where artefacts were revealed by low water levels in riverbed of Vistula river in Warsaw September 18, 2012. A huge cargo of elaborate marble stonework that sank to the bottom of Poland's Vistula river four centuries ago has re-appeared after a drought and record-low water levels revealed the masonry lying in the mud on the river bed. Archaeologists believe the stonework was part of a trove which 17th-century Swedish invaders looted from Poland's rulers and loaded onto barges to transport home, only for the booty to go to the bottom when the vessels sank. REUTERS/Kacper Pempel (POLAND - Tags: ENVIRONMENT SOCIETY)