Council staff and volunteers in Carlisle have begun packing up millions of historical documents.
The archives are to be transferred to a new £8.2m records office at Petteril Bank, which is due to open in 2010.
Some of the items date back to the 12th Century and include the Royal Charter of the City of Carlisle which bears the seal of Edward II.
The county archivist described the job as a "mammoth task" - the equivalent of moving 85 houses simultaneously.
Due to the work, the existing record office at Carlisle Castle will no longer be open on a Friday.
County archivist Anne Rowe said: "We hope for your understanding for the mammoth task we have in hand.
"Moving house is said to be one of the most stressful things you do in life, and moving the Carlisle archive collections is the equivalent of moving 85 houses simultaneously.
"To compensate, we will be in a position to provide you with much better services and facilities once we are operating from our new premises."