The Long Bridge consisted of 21 arches and was 840 feet in length. Many years ago Percy, a cracked poet, in one of his lucubrations added another arch to the Long Bridge, thus -
"Spanning the Lagan, now we have in view
The great Long Bridge, with arches twenty-two"
to which he appended a note-- "It has only twenty-one, but as a poetical licence, and for the sake of rhyme, I had to add another arch"
from: Guide to Belfast: The Giant's Causeway, and the Adjoining Districts of the Counties of Antrim and Down ... By William McComb 1861
This appears to be all that remains of the Long Bridge at the junction of Albertbridge Road and Castlereagh Street.
An old print of the Long Bridge.