25 ECU Ildefons Cerdá

Ildefons Cerdà's name rarely appears on currency, despite his 1859 Eixample plan for Barcelona being one of the most studied urban grids in architectural history. Spain issued this piece as part of a broader ECU commemorative program that flourished in the early 1990s before the euro rendered the unit of account obsolete — the ECU never circulated as physical currency anywhere, making the entire series a collector-only artifact from the moment of striking.