25 ECU - Beatrix Christiaan and Constantijn Huygens

The 1989 Dutch ECU series was part of a deliberate strategy by the Dutch Mint to position the Netherlands as a leading advocate for European monetary integration ahead of the Maastricht Treaty negotiations. Christiaan Huygens, the 17th-century mathematician and astronomer who discovered Saturn's rings and invented the pendulum clock, was a natural choice for a coin gesturing toward European intellectual unity — he worked extensively in Paris under Louis XIV's patronage while remaining a Dutch subject.

These ECU pieces had no legal tender status for everyday transactions but were recognized as collector currency. X#18.1 denotes the standard strikes; a proof variant was issued in the same year.