More than 1,000 demonstrators descended upon the Supreme Court Tuesday morning, voicing their opinions on gay marriage as the nine justices heard oral arguments on the first of two landmark same-sex marriage cases.

The morning started out calm, with hundreds of same-sex marriage supporters gathered on the sidewalks in front of the Supreme Court to hear speakers from United for Marriage: Light the Way to Justice, a coalition of marriage equality groups. Speakers included Del. Eleanor Holmes Norton, D-D.C., and Baltimore Ravens linebacker Brendon Ayanbadejo, among others.

Activists supporting same-sex marriage hoisted signs into the air with messages that included: “‘I do’ Support Marriage Equality,” “Tired of being a second-class citizen” and “Marriage equality equals economic equality.”

But at about 10 a.m., when the court began hearing oral arguments on Proposition 8 — a 2008 California ballot initiative that outlawed gay marriage in the state — a parade of hundreds of same-sex marriage opponents marched down First Street Northeast toward the court, igniting chants and arguments between the divided camps.

When the same-sex marriage opponents reached the Supreme Court, many knelt down in the middle of the street and prayed with their signs — which read “Every Child Deserves a Mom & Dad,” and “Kids do Best with a Mom & Dad” — while the crowd of same-sex marriage advocates began to loudly chant, “Gay, straight, black or white, marriage is a civil right.”

Eventually, the two groups faced each other. Some people from the pro-same-sex marriage rally approached their opponents to make their case, and vice-versa.

Capitol Police Public Information Officer Shennell Antrobus said Capitol Police made only one arrest, when a participant allegedly assaulted a police officer. But overall the event did not cause problems for the police force.

“It was a pretty controlled event,” Antrobus said.

Inside the court, justices seemed wary of making a broad ruling on same-sex marriage, with moderate Justice Anthony M. Kennedy appearing skeptical of the court entering “uncharted waters.” Instead, the justices seemed more likely to dismiss the case all together.

On Wednesday, the court will hear oral arguments in a second same-sex marriage case, this one challenging a provision of the Defense of Marriage Act Congress passed in 1996. Section 3 of DOMA says the federal government doesn’t recognize same-sex marriages awarded by state governments.

The court is expected to release its decision on both cases at the end of its session in late June.