Merkavah (‘chariot’) mysticism is the earliest form of Jewish mysticism, focused on visionary ascent through heavenly palaces (heikhalot) to behold the divine throne-chariot described in Ezekiel 1. Rooted in the apocalyptic traditions of the Second Temple period (Daniel, 1 Enoch), it survived 70 AD as an esoteric current within Rabbinic Judaism — carefully guarded, transmitted to select students, dangerous to the unprepared. The Talmud’s warning about ‘the four who entered the Pardes’ (Ben Azzai, Ben Zoma, Acher/Elisha ben Abuyah, Rabbi Akiva) encodes this danger. Merkavah mysticism eventually feeds into medieval Kabbalah through the Heikhalot literature.