(from lat. bractea “thin piece of metal”) coins or medals, struck only on one face, the pattern of which shows through on the reverse face.
The bracteates were usually called back regularly, they had to be exchanged for new coins with a deduction (Renovatio Monetae). This system worked like a demurrage: People wouldn't hoard their coins, because they lost their value. So this money was used more as a medium of exchange than for storing value. This increased the velocity of money and stimulated the economy.
Medieval bracteates were comon in Central Europe from 12th to 14. century, probably adopted from Danes or Slavic people. The coin trove of Kolomna could close this gap of evidence.

Монеты клада из Коломны 
 The coins of the Kolomna-treasure