The Wisdom of the Crowds

The same winter the Plataeans, who were still being besieged by the Peloponnesians and Boeotians, distressed by the failure of their provisions, and seeing no hope of relief from Athens, nor any other means of safety, formed a scheme with the Athenians besieged with them for escaping, if possible, by forcing their way over the enemy’s walls; the attempt having been suggested by Theaenetus, son of Tolmides, a soothsayer, and Eupompides, son of Daimachus, one of their generals. At first all were to join: afterwards, half hung back, thinking the risk great; about two hundred and twenty, however, voluntarily persevered in the attempt, which was carried out in the following way. Ladders were made to match the height of the enemy’s wall, which they measured by the layers of bricks, the side turned towards them not being thoroughly whitewashed. These were counted by many persons at once; and though some might miss the right calculation, most would hit upon it, particularly as they counted over and over again, and were no great way from the wall, but could see it easily enough for their purpose. The length required for the ladders was thus obtained, being calculated from the breadth of the brick.

— "The History of the Peloponnesian War" by our man Thucydides as rendered into English by the most righteous Richard Crawley

97. While they had these thoughts and had been set at enmity with the Persians, at this very time Aristagoras the Milesian, ordered away from Sparta by Cleomenes the Lacedemonian, arrived at Athens; for this was the city which had most power of all the rest besides Sparta. And Aristagoras came forward before the assembly of the people and said the same things as he had said at Sparta about the wealth which there was in Asia, and about the Persian manner of making war, how they used neither shield nor spear and were easy to overcome. Thus I say he said, and also he added this, namely that the Milesians were colonists from the Athenians, and that it was reasonable that the Athenians should rescue them, since they had such great power; and there was nothing which he did not promise, being very urgent in his request, until at last he persuaded them: for it would seem that it is easier to deceive many than one, seeing that, though he did not prove able to deceive Cleomenes the Lacedemonian by himself, yet he did this to thirty thousand Athenians. The Athenians then, I say, being persuaded, voted a resolution to despatch twenty ships to help the Ionians, and appointed to command them Melanthios one of their citizens, who was in all things highly reputed. These ships proved to be the beginning of evils for the Hellenes and the Barbarians.

— "The History of Herodotus" as laboriously translated by G. C. Macaulay on account of Herodotus being inordinately fond of words and many of them

Some context here is that the Spartan king (one of them, they had two because reasons) had said "yeah, no" about an expedition, however possibly profitable (Aristagoras having gotten himself into this mess by screwing up an in theory profitable operation that had left him deeply in debt), that would have taken the Spartan army three months away from the sea. For all their supposed might the Spartans were mighty shy about actually going out to fight on many occasions, possibly because the helots would (and did) revolt if they looked away for more than two seconds.

Anyways, the wisdom of the crowds may or may not work out. Where it does probably involves multiple measurements and comparisons and maybe some individual competition to get the most correct number (the former case, involving ladders). The latter case (where no ladders are known to be involved) shows how a crowd can be hoodwinked by a charismatic charlatan. Good thing we've learned since then!