London, Sep 19 (IANS): Thanks to a drought that dried up a Polish river, more than 10 tonnes of marble statues, fountains and palace pillars looted from Polish rulers, believed to be 400 years old, have been found stuck in mud at the bottom of the river.

The 10-tonne haul is believed to have been left behind by 17th century Swedish invaders during the Second Northern War in 1655, the Daily Mail reported.

The treasure was found on the bed of the River Vistula as its waters receded over the summer.

The Swedish invaders had loaded the treasure onto barges to transport home, but experts told the Daily Mail the masonry proved too heavy for their wooden warships that eventually sank under the weight.

The cargo remained stuck in mud at the bottom of the river for more than 400 years.

The period is known in Poland as "The Deluge".

One of Europe's most powerful armies, Swedish warlords swept through eastern Europe pillaging everything in their way. The armies also plundered Poland's riches.

Warsaw was so badly ravaged that its pre-war population of 20,000 was reduced to 2,000 by the time the Swedes set sail for home, the report said.

The drought also revealed unexploded mines from World War II and Jewish gravestones.

Historians believe the Swedes planned to move the looted cargo up the Vistula to Gdansk, where the river joins the Baltic Sea, and from there transport it home.

There is still no explanation as to why the boats sank on the way.