A historic 19th century document containing the names of 160,000 Irish residents is being published online for the first time.
Family history website Ancestry.com said Lord Viscount Morpeth's Testimonial Roll of 1841 measures 420 metres (1,378 feet).
It was presented to George Howard, the Lord Viscount Morpeth, when he left his post as chief secretary for Ireland in 1841.
Names and addresses on the document pre-date the Great Famine of 1845 and it has taken more than four years to digitise the information.
Miriam Silverman of Ancestry said: "Not only is the Morpeth Roll one of the most interesting and unusual records available at our site, but it's also one of the most valuable.
"The dearth of Irish census records means documents like the Morpeth Roll, which detail people's names and where they are from, can be used as a census substitute, helping millions find out more about their Irish ancestry."