Somewhere along the way I kind of picked up the idea that polygamy among Jews had mostly waned and was mostly non-existent by the time of the NT. I knew there was a formal ban much later, but I had it stuck in my head that that was pretty much just a formality. So the following comments from my friend Ben McGuire were of great interest to me, and I share them here by permission:
Polygamy was quite widespread at the time of the New Testament. This doesn’t mean it was exceptionally common, but it was widespread and widely accepted. Under Roman rule, women tended to have a greater degree of freedom with regards to these marriages (as they could file for divorce and such in civil courts – and it seems that at least on the Roman side, women could be represented by women attourneys – something you wouldn’t have seen prior to the Roman occupation in Judah).
For the most part, between the New Testament era and the first ban on polygyny (it was in the 11th century when Rabbenu Gershom issued The Ban – forbidding bigamy and divorcing a wife without her consent), the preferred method of preventing a husband from taking a second wife was to make stipulations against this practice in the ketubah (the marriage contract). And we have plenty of examples of these. There is also a lot of related (and valuable) documentation on this issue found at the Cairo Genizah (but sorting through all of it takes more patience than I have).
Gershom’s Ban was issued in Ashkenaz (11th century Franco-Germany). Later, takkanot would extend the authority of Gershom’s Ban to the point that it was considered just below Moses. Of course, most of the Jews in Islamic territories (where they were often given a high degree of autonomy) were opposed to the Ban for a number of reasons (but the arguments were primarily theological). Those who rejected the Ban most vocally were those of the school of Rabbenu Tam, and the most cited dissensions were those written by Speyer, Worms and Mainz. And the dissensions generally covered two points – the command to multiply and replenish the earth, and the fact that the Law of Moses required polygamy under certain circumstances relative to Levirate marriage.
The Jewish leadership in the early period of U.S. history was made primarily of Sephardic Jews (not Ashkenazic Jews), and so there was a significant amount of polygamy going on in the U.S. in the early years. In the U.S., a decision to ban polygamy occured at a rabbinic conference only as late as 1869 (note that this is when polygamy had begun to be a larger issue due in part to the Mormon question). However, even then, most U.S. Jews as late as the first decade of the 20th century still believed that polygamy was legitimate, and legal and binding.
Levirate marriage really didn’t begin to see a decline until the 13th century (AD), and in the 14th century, Rabbi Asher ben Jehiel ruled that as far as Ashkenazic Jewry was concerned, halitzah was no longer an optional practice in such cases, but a requirement (this is the situation in Israel today, but even modern Jewish courts hold that the brother-in-law is still obligated to the woman in the case of Levirate marriage until halitzah is performed, and she may not remarry until that happens either).
As far as New Testament times, some of the most interesting documents are a series of notes and letters found belonging to Babathah (in the Cave of Letters) dating to the time of the Bar Kochba revolt against Rome (132-135 AD). These documents (and others found by Yadin in the same place) really provide a tremendous amount of insight into the issues surrounding marriages, divorces, polygamy and so on.
Other evidence is more anecdotal (but still quite valuable). Rabbinic discourses (in the Mishnah) contain more than 100 clarifications of the practice of Levirate marriage, for example, most dealing with issues related to polygamy (what happens when sisters marry brothers, for example). It would seem rather absurd to see this volume of speculation based purely on hypotheticals. At the same time, in the period of time leading up to the ban on polygamy, there were attempts to limit the number of wives – primarily based on Deuteronomy 17:17, and the general consensus eventually ends up with the number four being a good number for the number of wives a man should be allowed to marry (following Jacob/Israel of course).