CONCORD, N.H. (AP) — Paper, the traditional gift for marking a couple’s first year of marriage, also is a great choice for 250th anniversaries — especially when filling a time capsule celebrating American independence.

The 2016 law creating the nonpartisan America250 commission mandated that a time capsule be buried in Philadelphia on July 4, 2026, and dug up 250 years later in 2276. Last week, the resulting 900-pound cylinder was sealed shut, capping years of technical design and construction, collaboration with states and meticulous review of collected items.

“Once it was closed, it was a little bit anti-climactic, and then it was kind of really emotional,” said Michael Berilla, who directs the fabrication technology office at the National Institute of Standards and Technology and led the team that designed and built the capsule.

Designed to stay dry

Berilla’s office, part of the Department of Commerce, has built encasements to protect historical documents in the past, but those tend to be stored indoors under carefully controlled conditions. With time capsules, the number one enemy is water, so much of the design work focused on how to keep it out.

The stainless steel capsule is shaped like a cylinder, not the typical box, because square edges tend to crack and break. It will be covered with a secondary cylinder that will trap air and push out any approaching water, and the capsule itself is rimmed with a soft metal that compresses under pressure.

“When you smash it shut with the lid, that metal goes into all the cracks and spaces and makes an airtight, watertight seal,” Berilla said.

The items inside were at 35% relative humidity. That’s moist enough to ensure they won’t dry out and disintegrate, but dry enough that they won’t create moisture problems. The capsule will be buried 10 feet below ground, safe from temperature fluctuations or storm damage, Berilla said.

“Philadelphia would have to be six feet underwater in order for this time capsule to even possibly take on water,” he said. “And if Philly is six feet underwater, you’ve got way bigger problems in the world.”

Filled with diversity

Inside the capsule are contributions from the three branches of the federal government, many of the ongoing America 250 events and programs, and all 50 states, the five U.S. territories and the District of Columbia. Most contents are in small archival boxes, while paper documents are in a separate compartment. According to a list posted on the America250 website Monday, archival quality paper was a particularly popular choice, with states submitting hundreds of letters, postcards, posters, poems and other printed material.

In a nod to its past, New Hampshire submitted a brochure featuring a timeline of major events in the state’s Revolutionary War history. California looked to the future, including the answer it got when it asked an AI ChatBot, “Write me a prediction of what California will be like 250 years from July 4, 2026.” Highways will be gone, grizzly bears will be back, and the entire state will secede and join Oregon, Washington and British Columbia to form the “Pacific Federation.”

Some states went all out. Utah sent 100 cards featuring historical citizens, 13 coins, eight documents, eight pins, two granite disks and a booklet. Arizona used nano-etching technology to put the full text of the Declaration of Independence and the U.S. Constitution on a stainless steel coin. Other submissions were more bare bones, literally. Maine’s submission included a bone from the endangered North Atlantic right whale. Arkansas sent a diamond.

The variety was fascinating, said Tom Medema, a retired National Park Service official and project manager for the time capsule.

“I’m glad there wasn’t really a prescription for it,” he said. “I know that was hard for them, but in the end, it was just up to them to represent themselves.”

Anything that might degrade or metals that would rust over time was forbidden: Maryland’s submission of Old Bay seasoning was rejected, while Native American beaded artwork backed by elk hide was resubmitted on a fabric background.

Some of the items reflect dark historical times, Medema said, as well as the nation’s current challenges. But an air of optimism still surrounded the project.

“There’s great hope in what this capsule represents and the messages that are put in it,” he said. “Something about this capsule has been truly uplifting for everyone who’s been involved in it.”

Looking back and ahead

This isn’t the first national time capsule tied to the anniversary of the signing of the Declaration of Independence.

A “Century Safe” filled in 1876 was opened by President Gerald Ford in 1976. That year in turn saw the creation of an official Bicentennial time capsule, which is stored at the National Archives and will be opened in 2076. And there’s another time capsule in the works that will be housed at the U.S. Capitol Visitor Center.

To ensure the America 250 capsule is found in 2276, the National Park Service has included details about it in its succession plans to be passed down through time. A capstone with information about it will cover the spot where it’s buried.

Berilla, who helped build the capsule, said when he thinks back to what America was like 250 years ago, he thinks about resilience.

“And when I think forward to the future, I hope that’s what they see from us,” he said. “That, yes, we had it hard compared to them, but more importantly, we were diverse. We were interesting. We were creative. We worked together.”

The capsule contains a photo of his team and a letter he wrote on their behalf.

“Greetings from the living, breathing hearts and hands of 2026,” Berilla wrote. “We will have long since returned to dust, but our devotion, pride, and unwavering hope for what our world could become are alive right here inside this steel. We built this for you.”

Holly Ramer, The Associated Press