Apocalypse is a Greek word meaning "Unveiling" and was originally applied to the revelation of the new Earth, new Heaven, and a new World - i.e. the Saturn System (The Otherworld) break-up and the creation of the present Solar System, along with the unveiling of the present Sun, Moon and the stars.

What we see enacted at Chichén Itzá on the Northern side of the Temple of Kukulkan is the global flood - caused by the collapse of the Earth-Saturn coiled Birkeland currents (i.e. The Feathered Serpent) - cascading down the World Mountain. To most of our ancestors, this is when their "Universe" (or a different sun) was created or unveiled and when time began. Later on, when the orbits of the planets had settled down, solar and lunar calendars could be calculated and formulated. But they still commemorated this one event that occurred some 5000 years ago. Most of the World's megalithic structures commemorate the Saturnian System in one form or another, whether for Saturn-Venus-Mars worship, sacrifice, burial or celebration; for obsessive observation of the much-feared ex-comet planet Venus; or for present Solar System time-keeping.

The beginning of the Apocalypse as symbolised by the Maya:
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Alternatively, it could be commemorating the Birth of Venus.