The letters of the Hebrew alphabet have played varied roles in Jewish religious literature over the centuries, primarily in mystical texts. Some sources in classical rabbinical literature seem to acknowledge the historical provenance of the currently used Hebrew alphabet and deal with them as a mundane subject (the Jerusalem Talmud, for example, records that "the Israelites took for themselves square calligraphy", and that the letters "came with the Israelites from Ashur "); others attribute mystical significance to the letters, connecting them with the process of creation or the redemption. In mystical conceptions, the alphabet is considered eternal, pre-existent to the Earth, and the letters themselves are seen as having holiness and power, sometimes to such an extent that several stories from the Talmud illustrate the idea that they cannot be destroyed.