500 Francs Lighthouse of Alexandria

Rwanda's National Bank has issued a long-running series of niobium-center bimetallic coins featuring the Seven Wonders of the Ancient World, with this Lighthouse of Alexandria entry appearing in 2013. The niobium core is colored during anodization — the oxide layer thickness determines the final hue, a process that produces consistent results only within tight voltage tolerances.

The Pharos of Alexandria, built under Ptolemy II in the 3rd century BC, stood roughly 100 meters tall and functioned for over 1,500 years before earthquake damage rendered it unusable by the 14th century.