Tradition has it that it was on this day, August 3rd, in 1492, that Christopher Columbus sailed out of Palos harbour in southern Spain on a voyage that transformed the world.
"The enterprise of the Indies" was, to put it mildly, an undertaking fraught with great uncertainty. Although people knew, in the late 15th century, that the Earth was round, they had no idea just how big it was. The accepted figure had been calculated as far back as 100 BC by the Greek astronomer Posidonius of Apamea.
His estimate was the planet had a circumference of 18,000 miles. So when Columbus embarked on his voyage, he reckoned that a mere 3,500mile westward voyage should take him by a back-door route to Marco Polo's fabled Indies and all the riches of the Orient.
The real distance to that destination, heading west, is a good 12,000 miles; had Columbus known this, he might have thought again about his venture.
Although judged by history to have been an inept administrator with no talent for political intrigue, Columbus was lucky with the elements. Or perhaps he was well informed; historians are divided on the point.
The story goes that years previously, in 1479, while visiting his brother-in-law, the Governor of Porto Santo in Madeira, Columbus noted the island was situated in a zone of northeasterly winds.
He is said to have put this observation to good use a decade later when planning his famous enterprise, by plotting a very southerly course to take advantage of the trades.
Once under way Columbus enjoyed ideal conditions on the journey. There were no storms or calms, and he made such rapid progress westwards that he was obliged to keep two reckonings of the distance covered. One of these he kept to himself; the other he announced to the crew - a deliberate underestimate to avoid their panic at having ventured so far into the unknown.
But in due course even the good weather became a source of anxiety for the crew. The weather was fine - but would it ever rain again, or would they die of thirst? The winds were steady - but would they ever find winds to blow them home again, or would the wind always blow from the east in these uncharted seas?
Only landfall on October 12th, 1492, 36 days after leaving the Canaries, pre-empted mutiny; on that day Christopher Columbus set foot on what he called Guanahani, believed to be the island that we now know as San Salvador.