Boyce--p. 74 said:
The three world Saviours
Another development which can be assigned to the Achaemenian period concerned the belief in the world Saviour, the Saoshyant. This belief became elaborated into an expectation of three Saviours, ea£:h to be born of the Rrgphet's seed by a virgin mother - an elaboration which appears to have been connected with a newly evolved scheme of world history, according to which 'limited time' (that is, the three periods of Creation, Mixture and Separation) was regarded as a vast 'world year', divided into segments of IOOO years each. This scheme, it is generally held, derived from Babylonian speculations about the recurrent 'great years', those spans of time which perpetually repeated themselves with all the events that had taken place in them . The texts vary as to how many millennia made up the Zoroastrian world year. Some give the figure as nine (three times three being a favoured number), others as twelve (corresponding to the months of the natural year). There are, however, grounds for thinking that the original figure was 6000 years, which was increased as priestly scholars developed the scheme. Of these 6000 years, the first 3000, it appears, were assigned to creation, the process of mixture, and the early history of mankind. Zoroaster himself was held to have been born towards the end of the third millennium, and to have received his revelation in the year 3 000. A time of goodness follows, and of progress towards the ultimate goal of creation, but thereafter men will begin to forget his teachings . In the year 4000 the first Saviour, named Ukhshyat-ereta, 'He who makes righteousness grow', will renew the prophet's gospel. History will then repeat itself, with his brother, Ukhshyat-nemah, 'He who makes reverence grow', appearing towards the year 5000 ; and finally, towards the end of the last millennium, the greatest of the Saoshyants, Astvat-ereta himself, will appear and usher in Frasho-kereti . This doctrine of the three Saviours further allowed priestly scholastics to fuse Zoroaster's message of hope with ancient Iranian traditions of humanity'S descent from a gold age - that of Yima - to the sorry present (assigned to the period of degeneracy before the coming of the first Saoshyant) ; and it gave them scope for elaborating patterns of recurring events. The whole scheme, of world chronology and the three Saoshyants, seems to have remained, however, a matter for the learned, while the people in general (to judge from later times) continued to look and long simply for the coming of the one Saviour foretold by Zoroaster.