400 is the square of 20 (the number of the letter Kaph and the simple sphere of Jupiter), a number of completeness, finality, and the sealing of a cycle. In Greek isopsephy, it is the value of the letter Upsilon (Υ, υ), whose name means “twisted” or “crooked,” symbolizing the forked path. The number 400 also corresponds to the Hebrew letter Tau (ת), the last letter of the alphabet, which has the literal meaning “mark” or “sign” and is shaped like a cross. Tau completes the Path of the Twenty-Second Letter, the lower path from Malkuth (Kingdom) to Yesod (Foundation) on the Tree of Life—the final step of the initiate’s ascent before crossing the abyss. The Greek Upsilon carries a similar terminal and decisive quality, associated with the life-or-death choice at the crossroads. In Greek numerical notation, 400 was written as Υʹ and could be combined with a lower stroke to form the stigma (Ϛ) for 6, but its independent significance remains that of a perfect square, an enclosing boundary. Esoterically, Tau as 400 relates to the fourfold nature of Malkuth (the Four Worlds and the four elements), and the cube of 400 (64,000) is the number of cubes in the Temple of Solomon according to some traditions, linking it to the solidity of the third dimension. In Liber 777, column CLXXXV (Numeration of Greek Alphabet) gives 400 as the thirty-second bis step, a supplementary value between the standard Path 32 (300) and the next regular step. This position highlights its role as a hidden or secret key—the number that fills a gap, the silent final letter that gives coherence to the preceding series. The table places it opposite the Hebrew value 300 and the Tzaddi paths, suggesting that whereas 300 (Shin, spirit) is the triadic fire that burns through the veils, 400 (Tau, cross) is the square stone that grounds and completes the structure.