The timeline was created as part of the Heart of the City refurbishment project, completed 2011.
A Northern Echo article on 2nd July 2011 reports the unveiling of the timeline. Quote from the article:
“Yesterday’s ceremony saw Durham County Council chairman Dennis Morgan, Durham Deputy Mayor John Wilkinson and schoolboy Stefan Szablewski unveil a timeline telling Durham’s history. Stefan, ten, was chosen because he suggested the timeline in a letter to the Durham Times in December 2009.”
Other websites have recorded the event – Ailsa Magnus ARBS – and described the artwork.