Botticelli's so-called "Birth of Venus" (aka: Venus on the Half Shell) is taken from Roman mythology (based on earlier Greek). She's seen rising from the waters riding a scallop shell with a bit of the sea foam evident that caused her birth. The shell symbolizes the ancient product of the water, which gave birth to us all. Various other pagan images adorn the painting. And Venus is the goddess of sexuality, so she's gonna be depicted a bit sexy, 'natch.
The knights' code of chivalry was based in, in part, courtly love -- a product likely brought to Europe from Persia. (A loaf of bread, a glass of wine and thou, &c.) Courtly love involved a strange practice of loving women from a distance, mostly the lady of the castle or manor, who was already spoken for.
BTW: the Botticelli painting is reprinted in ink transfer on a 2008 Cook Islands coin.
Here's some courtly love: