I picture knights in shining armor galloping on horseback through a field at dusk. One has a burlap sack full of silver coins on the back of his horse. Suddenly - an ambush! A group of thieves has engaged them in combat! The knights fight off the thieves but their sack of coins has been torn in the skirmish. Silver coins lay scattered everywhere. One of the knights fashions a torch. Through the flickering orange light they see their silver coins shimmering in darkness all over the field. The ground is wet this night and many of the coins have been covered by mud. The Knights scoop up as many coins as they can find and return to their castle.
For the next few days the King orders his subordinates to conduct a thorough search to recover as many of the coins as possible. After several days the king is pleased, 99% of the coins have been recovered.
This is how I'd like to think those silver coins got into that field, though it probably happened in a much less exciting way... like a peasant dropping his coin purse wile digging up a turnip.