The Peace Cross, he wrote, was and is a symbol of unity, noting that it included the names of both black and white soldiers at a time when the military was segregated.

“We can never know for certain what was in the minds of those responsible for the memorial,” Justice Alito wrote, “but in light of what we know about this ceremony, we can perhaps make out a picture of a community that, at least for the moment, was united by grief and patriotism and rose above the divisions of the day.”

In a concurring opinion, Justice Stephen G. Breyer said Justice Alito had eloquently set out why the Peace Cross could stay. But he added, quoting an earlier opinion, that other kinds of memorials could pose problems.

“The case would be different, in my view,” he wrote, “if there were evidence that the organizers had ‘deliberately disrespected’ members of minority faiths or if the Cross had been erected only recently, rather than in the aftermath of World War I.”

“A newer memorial, erected under different circumstances, would not necessarily be permissible under this approach,” Justice Breyer wrote.

In her dissent in Thursday’s two consolidated cases — American Legion v. American Humanist Organization, No. 17-1717, and Maryland-National Capital Park and Planning Commission v. American Humanist Association, No. 18-18 — Justice Ginsburg said the majority had undermined the separation of church and state

“Decades ago, this court recognized that the Establishment Clause of the First Amendment to the Constitution demands governmental neutrality among religious faiths, and between religion and nonreligion,” she wrote, quoting from Justice Alito’s opinion. “Today the court erodes that neutrality commitment, diminishing precedent designed to preserve individual liberty and civic harmony in favor of a ‘presumption of constitutionality for longstanding monuments, symbols and practices.’”