...We shall probably have to date the beginning of this development to about 2000 or 2500 BC - Moriz Winternitz

We cannot, however, explain the development of the whole of this great literature, if we assume as late a date as round about 1200 or 1500 B.C. as its starting point. We shall probably have to date the beginning of this development about 2000 or 2500 B.C... The more prudent course, however, is to steer clear of any fixed dates...

“… The passage [Śat. Br. II.1,2,3. …] in which we read that the Pleiades “do not swerve from the East” should probably not be interpreted as meaning that they rose “due east” (which would have been the case in the third millenary B.C., and would point to a knowledge of the vernal equinox): the correct interpretation is more likely that they remain visible in the eastern region for a considerable time – during several hours – every night, which was the case about 1100 B.C. [I am indebted for this explanation to Professor A. Prey, the astronomer of our University, who informed me that, in about 1100 B.C. the Pleiades rose approximately 13º to the north of the east point, approaching nearer and nearer the east line, and crossing it as late as 2 h 11 m after their rise, at a height of 29º, when seen from a place situated at 25º North latitude. They thus remain almost due east long enough to serve as a convenient basis for orientation. This interpretation of the passage is proved to be the correct one, by Baudhāyana-Śrautasūtra 27,5 (cf. W. Caland, Uber das rituelle Sūtra des Baudhāyana, Leipzig 1903, pp. 37 ff.), where it is prescribed that the supporting beams of a hut on the place of sacrifice shall face east, and that this direction shall be fixed after the Pleiades appear, as the latter “do not depart from the eastern region.” It is true that, about 2100 B.C. or about 3100 B.C., the Pleiades touched the east line earlier, but they proceeded southwards so rapidly that they were not suitable for orientation.] …”.

Oral tradition, too, presupposes longer intervals of time than would be necessary, had these texts been written down. Generations of pupils and teachers must have passed away before all the existing and the many lost texts had taken definite shape in the Vedic schools, On linguistic, literary and cultural grounds we must therefore assume that many centuries elapsed between the period of the earliest hymns and the final compilation of the hymns into a Samhita or “collection”, for the Rigveda-Samhita after denotes only the close of a period long, past, and again between the Rigveda-Samhita and the other Samhitas and Brahmanas, The Brahmanas themselves, with their numerous schools and branch schools, with their endless lists of teachers and the numerous references to teachers of antiquity, require a period of several centuries for their origin, This literature itself, as well as the spread of the brahmanical culture, theological knowledge, and not least, the priestly supremacy which went hand in hand with it, must have taken centuries, When we come to the Upanisads, we see that they too, belong to different periods of time, that they too pre-suppose generations of teachers and a long tradition.