Denier - Jean de Bethencourt countermark.

Jean de Bethencourt, a Norman baron who conquered the Canary Islands for the Castilian crown between 1402 and 1405, authorized a countermark on existing billon deniers to legitimize currency for his fledgling colonial administration — one of the earliest documented instances of European monetary adaptation in Atlantic colonization. The countermarked pieces circulated among a population that included Guanche islanders, Norman settlers, and Castilian soldiers, with no local mint infrastructure to produce fresh coinage.

Surviving examples are exceptionally rare and attribution can be contentious, as the countermark itself is often faint and the host coins vary.