The letter dal or dalet, means door in Hebrew. Its ancient glyph is this: 
This older glyph of dal is an image of a door hanging downward, like a curtain, able to swing in any direction. The door as symbol has a long and sacred history of representing thresholds and transitions between states of being or otherworlds. To help one move between realms, magic rituals would be performed and talismans would be placed within the threshold. The Jewish mezuzah, containing scripture passages, placed on doorways is based upon this same magic. Doors, gateways, and thresholds are considered sacred in many cultures.
Ariel Golan posits that the door represents transition, especially between the realms of the heavens and the underworld. Doors, or their equivalents, gateways, are found at places of thresholds. Golan discusses the worldwide prevalence of door/gates: “The Hittites built special gates to mark the boundary between sacral and secular areas . . . The Druids attached mystic significance to an entrance, to gates. Pagan Germanic tribes erected ritual gates. The ancient Egyptian temples and medieval Muslim mosques had hypertrophied façade walls whose forms emphasized the entrance . . . In Buddhism, there are free-standing gates of a religious significance. Symbolic gates were constructed in pre-Columbian America.”[i]
[i] Ariel Golan, Prehistoric Religion; 263.
