Scientists Cracked the Code on a 400-Year-Old Padlock. What It Was Protecting Is Still a Mystery.

3 min readA 16th-century brass padlock that secured treasure aboard the Ann Francis—an English merchant vessel used for smuggling—went down with the ship when it wrecked off the Welsh coast in a wild December 1583 storm. The padlock then lay hidden in the sand of Margam Beach for centuries. Even after a metal detectorist found it among the wreck’s hoard, its combination stayed a mystery—until now.“It’s not every day you get to solve a 400-year-old mystery,” said David Williams, a research associate at Cardiff University, in a statement.Williams works at the Musculoskeletal Biomechanics Research Facility at Cardiff University’s School of Engineering, where he typically uses his skills to study anatomy. This time, however, he looked deep inside the padlock, using micro-CT scanning to examine its internal mechanism without damaging it. The scans revealed the four-letter combination that opened the lock: ANCE.“By creating a detailed 3D image of the internal mechanism, I could see how the notches lined up with the letters and identify the exact combination,” Williams said. “We normally use this technology to study bones and other biological structures, so investigating a 400-year-old padlock was certainly a first for us.”After Williams sent the combination to the experts at Amgueddfa Cymru–Museum Wales, which cares for the Ann Francis treasure hoard, he could only wait to find out whether it worked. “Getting the message that we’d cracked it was incredibly satisfying,” he said.Alastair Willis, the museum’s senior curator for numismatics and the Welsh economy, said Elizabethan combination locks aren’t uncommon in Britain, but this one was in exceptional condition. Because the lock came from the Ann Francis, it can be dated precisely, which made it a “unique find and the code a tantalizing mystery to solve.”Still, questions remain. “Of course, now we’ve solved it we are left wondering if the code meant something to its owner,” Willis said. The team is also left to wonder exactly what the lock secured.The lock’s modern story began in 1996, when metal detectorist Peter Hughes discovered the wreck and part of the treasure it carried. For the next 21 years, Hughes kept returning to the beach, uncovering artifacts whenever dredging and storms stripped away layers of sand. His finds include rare gold coins from the reign of Ferdinand and Isabella of Spain, a boatswain’s whistle and other 16th-century coins. Among them was the padlock, which he found in 1999.“When I found the lock, I was immediately astonished by the incredible workmanship and its astonishing condition,” he said. “When I moved the ring dials of the combination they turned with ease after over 400 years beneath the sands and I was left in disbelief. I also remember being left excited at the prospect of finding wonderful things from the treasure chest it once locked.”Experts can only guess at what the chest held. Hughes found a collection of Spanish silver coins and two coin weights near the padlock, so the lock may have protected those objects. Or it may have secured a chest of other valuables, such as documents, that didn’t survive the wreck or the centuries that followed.The lock and the rest of the Ann Francis hoard are on display in the Tides of Treasure exhibition at the National Waterfront Museum in Swansea.That leaves one last mystery: What, if anything, did ANCE mean?Tim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland.