The find contained a mixture of extremely rare Anglo-Saxon coins and Viking silver, which provides a clearer understanding of the relationship between Alfred the Great, who ruled Wessex and his less well-known contemporary Ceolwulf II of Mercia.
Some of the coins were minted with a 'Two Emperors' design, borrowed from the Romans, which shows that the currency was used in both ancient kingdoms.
"This is an extraordinary find, one which re-writes Anglo-Saxon history," Xa Sturgis, director of the Ashmolean Museum in Oxford, which now houses the coins, told Sky News.
"The keeper of the coin room here came running up the stairs to tell me. The more they were excavated the more it became obvious how significant they are. These coins point to some sort of an alliance in the 870s between Alfred and Ceolwulf."
While Alfred is often described as the king who founded England, uniting Mercia and Wessex, very little is known of his rival Ceolwulf.
"These coins prove that there was a very real alliance between the two men at that time," added Julian Baker, coin curator at the Ashmolean.
"We can start re-writing that decade now, courtesy of the Watlington hoard."
The Ashmolean has until Monday, 31 January, to raise £1.35m to keep the coins and Viking silver in Oxfordshire and they are extremely close to that figure now.
More than 500 people in the local area have donated to the fund set up to raise the cash.
Mr Sturgis added: "Alfred is the only king in the history of England described as 'great'. But these coins show that in the 870s he needed Ceolwulf. It's incredible that we know so little about him and Alfred dominates everything. It's like he obliterated Ceolwulf."
The Watlington Hoard, as it is now known, is on public display at the Ashmolean as historians begin the process of re-assessing that period of Anglo-Saxon history.
SKY News.
