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Built in 1841, the Ouse Valley Viaduct (also called Balcombe Viaduct) over the River Ouse on the London-Brighton Railway Line north of Haywards Heath and south of Balcombe is 1,475 feet long.
The viaduct is 96 feet high and is carried on 37 semi-circular arches, each of 30 feet, surmounted by balustrades. Each pier contains a Jack arch with a semi-circular soffit to reduce the number of bricks required. At each end of the abutment is an ornamental square open tower, the brickwork of which is faced with stone from Heddon Quarries near Newcastle-upon-Tyne. The viaduct was designed by engineer for the line John Urpeth Rastrick in association with the architect of the London to Brighton railway, David Mocatta.

The Brighton Main Line opened in 1841. It operates between London (London Bridge and Victoria) and Brighton, it is 50 miles long. Today it is a very busy line as it includes trains to Gatwick Airport.
Wikipedia: Link

Listed buildings and structures are officially designated as being of special architectural, historical or cultural significance. There are over half a million listed structures in the United Kingdom, covered by around 375,000 listings.
Listed status is more commonly associated with buildings or groups of buildings, however it can cover many other structures, including bridges, headstones, steps, ponds, monuments, walls, phone boxes, wrecks, parks, and heritage sites, and in more recent times a road crossing (Abbey Road) and graffiti art (Banksy 'Spy-booth') have been included.

In England and Wales there are three main listing designations;
Grade I (2.5%) - exceptional interest, sometimes considered to be internationally important.
Grade II* (5.5%) - particularly important buildings of more than special interest.
Grade II (92%) - nationally important and of special interest.

There are also locally listed structures (at the discretion of local authorities) using A, B and C designations.

In Scotland three classifications are also used but the criteria are different. There are around 47,500 Listed buildings.
Category A (8%)- generally equivalent to Grade I and II* in England and Wales
Category B (51%)- this appears generally to cover the ground of Grade II, recognising national importance.
Category C (41%)- buildings of local importance, probably with some overlap with English Grade II.

In Northern Ireland the criteria are similar to Scotland, but the classifications are:
Grade A (2.3%)
Grade B+ (4.7%)
Grade B (93%)

Read more at Wikipedia Link