 Jain cosmology divides the worldly cycle of time into two parts ("avasarpiṇī" and "utsarpiṇī").According to Jain belief, in every half-cycle of time, twenty-four "tīrthaṅkaras" are born in the human realm to discover and teach the Jain doctrine appropriate for that era.The word "tīrthankara" signifies the founder of a "tirtha", which means a fordable passage across a sea.