Two pillars stood at the edge of the known world, and for centuries sailors read them as a warning: turn back, there is nothing beyond. One of those pillars is the lump of limestone you can watch turning gold at sunset from Europa Point. The other rises across the water in Africa. Between them runs a narrow blue gate that empires fought over, that myth said Hercules tore open with his bare hands, and that, according to one stubborn and seductive story, gave the world the most recognisable symbol in all of money. That symbol is the dollar sign. Trace the squiggle backward through ledgers and silver coins and royal coats of arms and you arrive, the legend says, right here at the Rock of Gibraltar. Whether the trail truly leads here is one of the genuine open questions of monetary history. The journey is worth taking either way, because it runs straight through this Strait. Long before banknotes, the entrance to the Mediterranean carried a name borrowed from Greek myth. The two headlands guarding the Strait were called the Pillars of Hercules. The northern Pillar, on the European side, is the Rock of Gibraltar, known to the ancients as Calpe Mons. The southern Pillar sits on the African shore, identified either as Jebel Musa in Morocco or Monte Hacho in Ceuta, a matter that scholars have argued about for centuries. The myth gives the geography a dramatic origin. In one version of his labours, Hercules was sent to fetch the cattle of the giant Geryon at the western edge of the known world. Rather than cross a mountain, the hero is said to have smashed through it, splitting the land and letting the Atlantic pour into the Mediterranean. The two halves left standing became his pillars. It is a tidy story for a real strait that does, in fact, separate two continents by only a few nautical miles at its narrowest. Stand at the right spot and you can see both shores at once, which is enough to make the legend feel less like a story and more like an explanation. > Smash a mountain in two and you do not just make a sea passage. You make a metaphor, a frontier marker that empires would later borrow and stamp onto their coins. Antiquity treated the pillars as the literal end of the world. A warning was associated with them: Non Plus Ultra, meaning nothing further beyond. The phrase captured a worldview in which the Strait of Gibraltar was the gate to the unknown, and sensible sailors did not pass it. For the classical mind, this was the edge of the map, and the open Atlantic beyond was a void to be feared rather than crossed. That caution made the pillars a natural emblem for limits. They marked where the familiar Mediterranean ended and the fearful ocean began. For most of recorded history, that was simply the truth of the matter. Then a Genoese navigator sailed west under a Spanish flag, and the truth changed overnight. After Christopher Columbus crossed the Atlantic, the warning at the world's edge began to look like an embarrassment. The young Charles, who ruled Spain from 1516 and later became Holy Roman Emperor Charles V, adopted a personal device that turned the old caution on its head. On the advice of his physician and counsellor Luigi Marliano in 1516, he took the motto Plus Ultra, further beyond, and paired it with the two Pillars of Hercules. The symbolism was deliberate and rather brilliant. The pillars that once said stop now framed a banner urging the empire onward, beyond the Strait, beyond the Atlantic, into a New World the ancients never knew existed. Charles V placed the two columns, wrapped with scrolls reading PLUS and ULTRA, as supporters flanking the Spanish royal shield. The monument to limits became, with two words, a monument to ambition. That single edit to an old motto is the hinge on which this whole story turns. Heraldry is one thing, but the pillars escaped the coat of arms and travelled the globe by a far more powerful vehicle: hard currency. Spain minted a large silver coin worth eight reales, the real de a ocho, known in English as the Spanish dollar or, more romantically, as pieces of eight. From the late fifteenth century onward, this coin became the closest thing the early modern world had to a global reserve currency, accepted from Manila to Boston and trusted by people who could not read a word of Spanish. Certain issues carried the pillars prominently. The coins struck from 1732, the columnario or Pillar Dollar series, showed the crowned Spanish arms supported by the two Pillars of Hercules on the reverse, the columns draped with a ribbon bearing the words PLUS ULTRA. Minted in vast quantities in the New World, especially at Mexico City, they circulated for decades and were so trusted that the United States later modelled its own dollar on them. The Spanish dollar remained legal tender in America until the Coinage Act of 1857 finally withdrew the privilege from foreign coins. Here is where the symbol enters the story. Look at the pillars on the coin and you see two vertical columns