2 Chronicles 36:21

See the marginal references. The 70 years of desolation prophesied by Jeremiah, commenced in the fourth year of Jehoiakim (Jeremiah 25:1, Jeremiah 25:12; compare Daniel 1:1), or 605 B.C.; and should therefore have terminated, if they were fully complete, in 536 B.C. As, however, the historical date of the taking of Babylon by Cyrus is 538 B.C., or two years earlier, it has been usual to suppose that the Jews reckoned “the reign of the kingdom of Persia” as commencing two years after the capture of Babylon, on the death or supersession of “Darius the Mede.” But the term “seventy” may be taken as a round number, and the prophecy as sufficiently fulfilled by a desolation which lasted 68 years.

Until the land had enjoyed her sabbaths - Between the time of Moses and the commencement of the captivity, there had been (about) 70 occasions on which the Law of the sabbatical year Leviticus 25:4 had been violated.