During the 7th and 8th century a type of silver coin, known as a sceatta (pronounced sheatta) was minted in a variety of locations throughout the North Sea.

Unlike the standard coinage of the period (gold coins minted by Merovingian kings for instance) these coins lack any royal, geographical, or "national" (I use that term very loosely) connection or inscription. Instead they had various types of images, so that we tend to type them by these images.

For instance, the [Wodan/Monster type] (http://www.nederlandsemunten.nl/Virtuele_munten_verzameling/Angel_Saxisch/Verzam_Zilveren_sceat_X_serie_Wodan_monster_type_710-760-5.jpg) or the Porcupine type

As I said, these coins were minted in a variety of places, including England, Frisia (modern day Netherlands), Francia, and Scandinavia and they appear to have been used as part of an "extra-national" trade network that was developing at this time. We find collections of them spread across the North Sea at central places (i.e. trade sites) and also in hordes. Silver coins of less weight and value than gold coins could more easily be minted in Europe and more easily spent, and the fact that they weren't "national" meant that they could be used across borders more easily, since they would not have to be exchanged or valued against local coinage.