El Hierro

For three centuries longitude was counted from the edge of the known world.

Ferro is the old name for El Hierro, the westernmost of the Canaries and the last land Europeans knew of before the Atlantic. Ptolemy had put his zero at the Fortunate Isles, and a French decree of 1634 confirmed the choice; it was later defined as exactly twenty degrees west of Paris. German and Austrian maps were still printing longitudes from Ferro into the twentieth century.