A restoration project for Durham Castle is to benefit from a £900,000 cash boost.
The castle and cathedral are World Heritage sites
The Northern Rock Foundation is giving £450,000 to the scheme for the World Heritage site.
The University of Durham is to match the cash, which will allow the first phase in a long-term repair and conservation programme to begin.
The initial work will focus on the roof structure of the castle and is part of a larger £7m project.
Durham University is the custodian of the castle, which was founded in 1072.
Vice-chancellor Sir Kenneth Calman, said: "This is a tremendous demonstration of support for the heritage of the region."
Sir David Chapman, a trustee of Northern Rock Foundation, added: "The Castle is one of the major architectural treasures of Europe and an instantly recognisable symbol of the North East.
"Our investment gives the restoration work the initial boost it needs, and the profile that will help bring other investors on board."
The project will begin later this year and involves major conservation work to the leaky roof, installed in 1840, above the castle's Norman Gallery and the wing with the oldest parts of the building that date back to the 1070s.
The original roof was put in place in 12th century, and age and weathering have meant that both slates and stonework have decayed.
Restoration will minimise further damage to the internal walls, ceilings, floors and contents in an area which is a main part of the visitor tour of the castle.
Durham Castle was a home and seat of administration for the former Prince Bishops of Durham until 1837, when it was provided as accommodation for the University, then only five years old.
It is the oldest building in the UK used for student accommodation, with105 of the college's current students living there.