THE State will be forced to spend up to half a million euro digging up the site of a proposed 'superprison' in north Dublin after five areas of archaeological interest were found there.
Despite the Government previously stating that "nothing" of significance had been discovered at Thornton Hall, the Irish Prison Service has now admitted that extensive investigations will have to be completed before the prison can go ahead.
The move comes after former Justice Minister Dermot Ahern said in May 2008 that despite "extensive and careful" archeological investigation of the site, "nothing of significance has been discovered".
But among the potential finds are a large hilltop enclosure, dating from the seventh century, and a settlement dating from 2000BC. Pottery and a stone axe-head have also been recovered.
More than €43m has been spent so far on the Thornton Hall prison complex, which sparked controversy in 2005 when it emerged the State had spent almost €30m on a 150-acre site on the Dublin/Meath border, or €200,000 an acre -- at a time when land nearby was selling for €26,000 an acre.
The prison is designed to replace the overcrowded Mountjoy Jail, and will be built under a public/private partnership.
A dedicated access road and security fence is currently under construction, and the first 400 cells are due to open in 2014.
The project was approved by the Dail in 2007, and an extensive archeological investigation was completed over 20 weeks from December 2005 to April 2006.
The findings are contained in a document called an Environmental Impact Assessment (EIA), completed in February 2008, which noted: "Of 36 sites of potential cultural heritage . . . eight were identified as requiring further investigation prior to construction."
Despite this finding, in May 2008 the then Justice Minister Dermot Ahern stated: "Nothing of significance has been discovered."
Experts use a number of methods to find sites of archeological interest, including searching documents, carrying out visual inspections and completing geophysical surveys.
Tender documents published by the Irish Prison Service state that "several large features" were detected, which consisted of three enclosures, a possible enclosure, a possible ring ditch, a likely modern curved anomaly and the remains of a laneway that had been evident on maps.
The large hilltop enclosure dates from the seventh century and includes drainage ditches running down a slope, indicating it could be a settlement. Fragments of a bracelet were found nearby.
A second site indicates a drainage system, possibly serving the hilltop enclosure.
A third enclosure dates from the late neolithic period, with previous investigations indicating it dates from 2880BC to 2580BC. Pottery and a stone axe-head were recovered.
Another site could be a moated settlement from the Anglo-Norman period.
If anything of significance is found the Government has a number of options.
It can preserve by record -- meaning the find is photographed and artifacts removed before construction work begins -- or they can be left in situ, which could lead to problems building the prison.