WASHINGTON -- The federal judge who struck down Wisconsin's gay marriage ban thinks state officials have a thing or two to learn about the history of marriage as a social institution.

In defending their same-sex marriage ban, state officials claimed that "virtually all cultures through time" have recognized marriage "as the union of an opposite-sex couple."

But as U.S. District Judge Barbara Crabb wrote in her 88-page ruling on Friday, that's simply not true.

"As an initial matter, defendants and amici have overstated their argument. Throughout history, the most 'traditional' form of marriage has not been between one man and one woman, but between one man and multiple women, which presumably is not a tradition that defendants and amici would like to continue," Crabb wrote in her opinion.

History alone wasn't enough to justify a ban on same-sex marriage, Crabb said.

"Like moral disapproval, tradition alone proves nothing more than a state's desire to prohibit particular conduct," she wrote, citing Justice Antonin Scalia's dissent in a 2003 sodomy case, which stated that "'preserving the traditional institution of marriage' is just a kinder way of describing the State's moral disapproval of same-sex couples."