The Supreme Court ruled unanimously on Monday that the city of Boston violated the Constitution when it refused to let a local organization fly a Christian flag in front of city hall.

While the case had religious overtones, the decision was fundamentally about free speech rights. The court said the city created a public forum, open to all comers, when it allowed organizations to use a flagpole in front of City Hall for commemorative events. Denying the same treatment for the Christian flag was a violation of free expression, it said.

"When the government encourages diverse expression — say, by creating a forum for debate — the First Amendment prevents it from discriminating against speakers based on their viewpoint," Justice Stephen Breyer wrote in the decision.

"The city’s lack of meaning­ful involvement in the selection of flags or the crafting of their messages leads us to classify the flag raisings as pri­vate, not government, speech — though nothing prevents Boston from changing its policies going forward," Breyer added.The ruling was a victory for a group called Camp Constitution, which says part of its mission is “to enhance understanding of the country’s Judeo-Christian heritage.” The group wanted to raise a flag bearing a Latin cross during a one-hour event that would include speeches about Boston’s history from local clergy.