Massachusetts on Sunday celebrated the 15th anniversary of the landmark decision which legalized marriage equality in the commonwealth.

On November 18, 2003, Massachusetts became the first state in U.S. history to declare a state ban on gay and lesbian couples marrying unconstitutional.

Then-Governor Mitt Romney, a Republican and the U.S. Senator-elect from Utah, attempted to reverse and undermine the Supreme Judicial Court's ruling.

In 2015, the U.S. Supreme Court found in Obergefell v. Hodges that gay couples have a constitutional right to marry, striking down state laws and constitutional amendments that defined marriage as a heterosexual union.

(Related: Jim Obergefell says he doesn't trust Trump on marriage equality.)

Mary Bonauto, civil rights project director at Gay & Lesbian Advocates & Defenders (GLAD), was the lead attorney in the lawsuit which struck down the prohibition in Massachusetts. She also argued before the Supreme Court in Obergefell.

“With more same-sex marriages, you saw more people changing their minds,” Bonauto told the AP in 2013. “Seeing gay people with their extended families, seeing the commitment, that's what has turned this around.”

Robert Compton and David Wilson, now married. were two of the 14 plaintiffs in the case.

“I was confident we were going to win, and when we won, I was just totally elated,” Compton told NBC News.

Wilson said that they joined the lawsuit because they were thinking about how they could protect each other in retirement. He said that he was not allowed to be by Compton's bedside when he was hospitalized because they were not married.

“It was things like that that made me aware that you might not have all the rights you think you do,” Compton said.

The men said that during the highly publicized case they received death threats.