A well which was the main source of water during the 1688-89 Siege of Derry has been discovered in the centre of the city.
The well, which is eight feet wide and at least 40 feet deep, has been perfectly preserved and has been described by an archaeologist as being as significant in historical terms as the walls of Derry.
Builders carrying out renovation work in Bishop Street found the well when they lifted a manhole cover at the junction of Bishop Street and London Street. Department of the Environment archaeologist Mr Paul Logue said it was a very important piece of the city's history.
"Wells are quite hard to date but this one was certainly here during the siege because it is actually shown on a siege map drawn at the time. How far back it does go I'm not too sure but it could go back to the 14th century. It is a vital piece of the city's history because it relates directly to the siege and in some ways it's just as important as the walls in terms of being a marker of what people did in those times.
"This was the main drinking well during the siege. Water then was critical for the people inside the walls who were under siege from the Jacobite army outside, in fact water was even more important than food. We know that during the siege many people fled into the city within the walls and this main well then became overused and therefore the water became muddy and dirty. We also know that a lot of people who used this well lost their lives queuing up for water because the Jacobites frequently fired mortars and cannon balls into the city centre which killed large numbers of the population.
"When the water became undrinkable during the siege, the people inside the walls had to look elsewhere for their water and the other main source was at St Columb's Wells in the Bogside.
"But that was in the vicinity of the Jacobite army so when people made daily raids in an attempt to bring back water inside the walls, they paid a very heavy price for doing so.
"This is a terrific well, right in the heart of the city. We'll now survey it, seal it and preserve it," said Mr Logue.