Nearly all the nude Venuses you see in halls and gardens around the world derive from one: the VENUS of CNIDUS by Praxiteles. (Also called the Aphrodite of Cnidus. Aphrodite and Venus are the Greek and Latin names for the same goddess).
An ancient copy of the Aphrodite of Praxiteles, restored by Ippolito Buzzi (Italian, 1562–1634) (public domain photo)
She was the nude—THE Venus.
The Capitoline Venus, the Medici Venus, the Venus of Milo—they are all modified copies of Praxiteles’ original statue. Even the cute Esquiline Venus is a take-off on her. [The archaeologist and classical scholar Judith Weingarten has convinced me that the Esquiline Venus is NOT based on Praxiteles' Aphrodite. See her post on Cleopatra.]
The so-called “Esquiline Venus”, first century BC (Creative Commons Attribution-Share Alike 3.0 Unported license photo)
What happened to the original?
It was lost, maybe while in hiding during an invasion or war.
Are the copies good?
No. They vary from so-so to very bad. Apparently, casts from the original could never be taken because the Venus was polychromed (painted) and the plaster casts would have ruined the paint. So sculptors had to copy with their eyes alone.
Detail : photo by © Marie-Lan Nguyen / Wikimedia Commons (Creative Commons Attribution 2.5 Generic license)
What is the Venus doing?
She has just taken off her clothes and is about to have a ritual bath to restore her virginity.
No one sees and yet she modestly tries to cover her genitals with her hand. So she was known as the Venus Pudica (Modest Venus).
Later copies (the Capitoline Venus, the Medici Venus) have her trying to cover her breasts (not very successfully) with the other hand.
So-called Capitoline Venus, Rome (public domain photo)
This modification increased her voluptuousness and was, they say, a concession to the corrupted tastes of the rich patrons of later times.
The limbs of stone statues break off in time. Maybe an artist who was ordered to restore her arms, and who hadn’t seen the original, supposed the Venus had been trying even harder to cover up her nakedness by using both arms and hands. In that case he never intended the new pose to be an alteration, let alone an improvement. But now the Venus Pudica seems to call attention to just those parts of her anatomy which she is trying to hide.
The original gesture of modesty was probably an invention of Praxiteles. It was very unlikely that it was copied from his model, the courtesan Phryne.
Why was the Praxiteles’ statue such a hit?
He belonged to a generation of artists that began to humanize the gods. A naked Venus was a new, even a scandalous idea. The story goes that Praxiteles got an order for a Venus from a city called Kos and made two statues, a clothed one and a naked one so the citizens of Kos could choose. They were shocked by the naked Venus and chose the clothed version for their temple. You didn’t put a naked goddess in a temple!
But citizens of another city, Knidos or Cnidus, were quick to see the “virtues”of the naked Venus and bought it from Praxiteles. They put it in their little round temple and it became famous—it put Knidos on the map. Tourists from all over flocked to see it. And those endless copies were made.