Tom Moore got the call just before Christmas in 2021. The head of the University of Durham’s Archaeology department, Mr. Moore was well-known in history circles in Yorkshire, in northeast England. It was why he had received the urgent message, from a man who claimed to have stumbled on something big.

“I think it’s Iron Age,” said the caller, Peter Heads, an amateur metal detectorist. And then, no one said a word.

Now, after more than three years of painstaking excavation, conducted in near-total secrecy, Mr. Moore and his colleagues say that it could be one of the most significant archaeological finds in northern England — and could change historians’ understanding of the Iron Age, around 2,000 years ago.

“Quite simply, this is one of the most important and exciting Iron Age period discoveries made in the U.K.,” Duncan Wilson, the chief executive of the government agency Historic England, said in a statement this week. “It sheds new light on Iron Age life in the north and Britain, but it also demonstrates connections with Europe.”

Since Mr. Heads’s finding in 2021, a team of archaeologists working at the site has collected a total of more than 800 objects, most dating to the Iron Age. Among them are cauldrons, a wine-mixing bowl, coral-coated horse harnesses and ceremonial spears.

They also include 28 iron wheels, presumably from a chariot or wagon — the kinds of transportation mechanisms never before believed to have existed in such size and scope among the elite of Britain’s Iron Age.