The talented members of Hyndburn and the Ribble Valley Dectorists Club unearthed 83 coins and two bracelets during a dig at a farm near Gisburn on Saturday.
The coins of various types have now been handed over to the local Finds Liaison Officer who will inform the local coroner and commence the treasure case.
Delighted member Andrew Smith, from Clitheroe, said: "This could be the biggest hoard of Roman coins ever found in the Ribble Valley. We will have further details on the coins and the two bracelets when the treasure case starts moving forward, but this is a significant and exciting find.
"It was two of our members Andrew Winter and Andy Bijsterbosch who came across the hoard. With assistance from club marshals and admins, we eventually unearthed a huge haul.
The club chairman Jon Ferguson and his team have had numerous hoard and treasure cases over the past few years from all over the Ribble Valley.
Members meet every first Tuesday of the month at the New Inn pub in Clitheroe.