The Blackfriars or Dominican Friary was founded in the second quarter of the 13th century, perhaps by Isabel, Countess of Arundel. Friars liked to live close to the people they were preaching to, and here they were beside not only the river crossing but also the port and the market. Many other friaries had low-lying sites on the edge of the town or city, for instance the London Blackfriars.
The function of the surviving south range is not clear, but since it was a two-storeyed it cannot have contained the church; that must have been in the north range, remains of which can be seen behind the public lavatories opposite. The west range, which has largly gone, may have included the dormitory. Nothing is known about the east range if there was one.
After the Friary was dissolved in 1538 its buildings were converted to other uses: the south range for a time contained a timber yard and the west range a malthouse. Mill Road was laid out across the site in 1894. The remains of the south range were given to the town by the 16th Duke of Norfolk in 1935.
(The buildings were previously wrongly identified as the hospital of the Holy Trinity or Maison Dieu, which in fact stood west of St Nicholas's churchyard.)
For further reading, see article by Timothy Hudson in Country Life, 12 July 1990.
The information board also shows a plan of the priory and other buildings and it can be seen that this is only a small part of it.