Justice Elena Kagan agreed that for many people, a cross is a "very natural way" for people to mourn those who have died, and that it carries a different meaning in the context of World War I.
There are numerous other cross-shaped monuments on public land, including at Arlington National Cemetery.
The American Humanist Association and a small number of Prince George's County residents filed suit against the park and planning commission and the American Legion in 2014, and argued that a cross-shaped monument on public land was a violation of the First Amendment's Establishment Clause.
The two cases were consolidated into one when the Supreme Court granted certiorari and agreed to hear the case.
The lawsuit was originally brought in 2014 and rejected by the District Court, which held that it was "uncontroverted" that the maintenance and display of the memorial was not "driven by a religious purpose whatsoever."
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In 2017, the Fourth Circuit Court of Appeals ruled that the monument was unconstitutional. In November of 2018, the Supreme Court granted certiorari.
The monument's construction was funded by mothers of the dead servicemen as well as the American Legion. The cross contains a plaque bearing the names of 49 Prince George's County men who were killed in the war.
The American Legion's logo is featured prominently on the cross, along with the words "valor," "endurance," "devotion" and "wisdom."