5 Euros - Henri I Château de Esch sur Sûre

Luxembourg's bimetallic niobium series, launched in 2004, was designed to compete directly with Austria's highly successful niobium commemorative program. The blue coloration of the niobium core is achieved through anodization — a controlled oxidation process that produces a precise wavelength of light interference rather than any applied pigment. Esch-sur-Sûre's castle ruins date to the tenth century, perched on a narrow peninsula nearly encircled by the Sûre river, and the site remained a seat of the local counts until the male line died out in the thirteenth century.