In ancient Greece, it was common for people to consult "mirror seers," who told their fortunes by analyzing their reflections. As the historian Milton Goldsmith explained in his book "Signs, Omens and Superstitions" (1918), "divination was performed by means of water and a looking glass. This was called catoptromancy. The mirror was dipped into the water and a sick person was asked to look into the glass. If his image appeared distorted, he was likely to die; if clear, he would live."
In the first century A.D., the Romans added a caveat to the superstition. At that time, it was believed that peoples' health changed in seven year cycles . A distorted image resulting from a broken mirror therefore meant seven years of ill-health and misfortune, rather than outright death.