Both sides of the national gun debate are poring over history books to try to bolster their case on whether residents of the nation’s capital can more freely carry guns on the street.

On Friday, in a possible preview of a U.S. Supreme Court showdown, a federal appeals court in Washington will hear a challenge to a law that restricts who can legally carry a handgun outside the home.

A key question in the case is whether such regulations have “long-standing” precedent. That has led lawyers to comb through historical documents for examples of how guns were used during the colonial era and earlier, in England during the Middle Ages.

The lawyers are taking the unusual step with the U.S. Supreme Court clearly in mind. No matter the outcome in the case on appeal, many legal experts think the high court will soon have to step in to more clearly settle whether and to what degree the Second Amendment protects the right to carry handguns outside the home—a question the justices have yet to address.

The emphasis on historical events makes sense given how “deeply the current Supreme Court considers history in some of its rulings,” said Adam Winkler, a law professor at the University of California, Los Angeles, and an expert on gun laws.