ECU

On 13 March 1979, the European Currency Unit (ECU) or European unit of account was introduced. This was a forerunner of the euro, a 'basket currency', meaning that the currencies of the various European member states were taken together, with the share of each currency in the basket being determined by the economic strength of each state. (Source: Wikipedia)

Apparently, a lost coin because who knows what?
The currency would have a value of 1 Euro. Currently, it is only a collector's item.