It is believed that the structure of Borobudur symbolized three cosmic realms (called triloka or tridhatu): kamadhatu, rupadhatu, and arupadhatu.
These three sections are each divided into three levels, so there are a total of nine levels.
These three sections correspond to:
(1) the world of desire (rebirth in samsara; kamadhatu),
(2) the realm of forms (renouncing greed, as a result of meditation, but still moderately attached to the everyday world),
(3) the realm of formlessness (enlightenment and nonattachment to the material world, as the outcome of sustained meditation).