The Queen and Duke of Edinburgh were shown around a £19 million state-of-the-art resource centre.
Her Majesty officially opened The Keep, near Falmer, which will provide a home for archives and historical resources of East Sussex and Brighton and Hove.
Archivists showed the royal delegation maps of Sussex from 179, historic pictures of Eastbourne before it became a resort.
Other achived included photos of Brighton Carnival stretching along Madeira Drive and its oldest document, Battle Abbey Charter, from 1101.
Senior Archivist Chris Whittick said: “They both showed a great interest in what he had shown them and they made most perceptive comments.
“We tried to select documents that would be of interest but not too personal. I think we got the right balance.”
Around two hundred royal watchers waited at Woollards Field, Moulsecoomb, for the royal cavalcade to arrive.