At this point they came in sight of thirty forty windmills that there are on plain, and as soon as Don Quixote saw them he said to his squire, "Look there, friend Sancho Panza, where thirty or more monstrous giants present themselves, all of whom I mean to engage in battle and slay, and with whose spoils we shall begin to make our fortunes; for this is righteous warfare, and it is God's good service to sweep so evil a breed from off the face of the earth."
"Look, your worship," said Sancho; "what we see there are not giants but windmills, and what seem to be their arms are the sails that turned by the wind make the millstone go."
"It is easy to see," replied Don Quixote, "that thou art not used to this business of adventures; those are giants; and if thou art afraid, away with thee out of this and betake thyself to prayer while I engage them in fierce and unequal combat."
He gave the spur to his steed Rocinante and made at them shouting, "Fly not, cowards and vile beings, for a single knight attacks you."
A slight breeze at this moment sprang up, and the great sails began to move, seeing which Don Quixote exclaimed, "Though ye flourish more arms than the giant Briareus, ye have to reckon with me."
With lance in rest and covered by his buckler, he charged at Rocinante's fullest gallop and fell upon the first mill that stood in front of him; but as he drove his lance-point into the sail the wind whirled it round with such force that it shivered the lance to pieces, sweeping with it horse and rider, who went rolling over on the plain, in a sorry condition.
–– Miguel de Cervantes, Don Quixote (translated by John Ormsby, excerpt edited and abridged by Bard)
The complete text can be found at Wikisource