That, and the fact the Thames passes through the heart of London, makes the waterway's foreshore (the riverbank exposed between high and low tide) one of Britain's most important archaeological sources, according to Forsyth, the Museum of London curator.
"Thames was the main conduit for transport and travel," Forsyth said. "People relied on boats to get between the north and south banks, and there were lots of smaller boats carting cargoes. Accidents would occur and things would fall overboard."
Forsyth says another prime source for objects found along the Thames today, outside boating accidents of centuries past, is ancient domestic rubbish. Such trash, which included old or broken toys, was used to backfill timber revetments, or embankments, built along the river up to about 1500.
"Every 25 years, on average, these revetments needed to be replaced. So over centuries, deposits of rubbish built up on the foreshore," Forsyth said.
Today, the tidal drop in the River Thames in London can approach 25 feet (7.62 meters), leaving large areas of mud exposed each day.
Founded in 1980, the Society of Thames Mudlarks has some 70 members. Forsyth says they are publicity shy. Under the licensing agreement allowing them to go metal detecting along the Thames, however, they must report historical finds to the Museum of London.
"We don't want people to go down there and think they can recover things willy-nilly," Forsyth said. "There's been a certain element of underworld activity. So we have to be cautious. It's also a very dangerous environment. You need to know your tides and to go with somebody else."
The museum now holds around 1,000 Mudlark finds, though not all are made from pewter. Many of the miniature guns and cannons were once working replicas and consist of copper alloy to withstand firing pressures.
"The largest of them are equivalent to a pocket pistol. So [they're] perfectly capable of killing somebody," Forsyth said. "It's obvious they are not perfect replicas. But we know they worked, because some of the barrels have exploded."
"If these were being used by children, then they probably met with an unfortunate accident. Certainly children had access to black powder and could use all sorts of projectiles," she said.
The miniatures weren't the only playthings that worked. For instance, tiny copper cauldrons have been found with sooty bases, suggesting children used them to cook food.
Hobbs says other replicas, including a three-legged stool, a birdcage, and tools such as saws, are important because no previous record of these objects is known for the period. "It enriches what we know about the medieval household in terms of the contents of a house," he said.
Some miniatures are so detailed that Forsyth suspects they were probably made for adults who wanted a copy of possessions of which they were particularly proud.
"One classic example is a standing buffet," she said. "It would have been made up from a flat shape that folded up into a three-dimensional form. It's extremely intricate and very cleverly designed."
Despite the exhibition's title, Hobbs notes Buried Treasure isn't just about objects made of silver or gold. True treasures are those that illuminate the past, he says.
Buried Treasure will appear at The National Museums and Galleries of Wales, Cardiff, from May 14 to September 5, before moving on to Manchester, Newcastle, and Norwich.
SOURCES AND RELATED WEB SITES