People have been looking at their own images in pools of water since there have been people, but you don't get a really good view that way. Polished metal was an improvement, then glass, but a really clear look at oneself requires a mirror. These came about at around 1300 CE, and proved to be a game changer as they spread through the world in the 15th century. Before mirrors, people identified themselves as part of a group, because their experience of self was mainly in relation to those around them.
This is why the medieval punishments of banishment and exile were so severe. A tradesman thrown out of his hometown would lose everything that gave him his identity. He would be unable to make a living, borrow money, or trade goods. He would lose the trust of those who could stand up for him and protect him physically, socially, and economically. He would have no one to plead his innocence or previous good behavior in court, and he would lose the spiritual protection of any church guild or fraternity to which he belonged. What happened in the fifteenth century was not so much that this community identity broke down, but rather that people started to become aware of their unique qualities irrespective of their loyalty to their community. That old sense of collective identity was overlaid with a new sense of personal self-worth.
But the transition was not for everyone at once. Mirrors were expensive, and only the wealthy had the means to perceive themselves as individuals at the time. Royalty, artists, philosophers, and scientists led the way, with common people following over time, as you'll read in an article at Lapham's Quarterly. -via Digg