Groundwork for the construction of 8,000 homes at Cherrywood in south county Dublin is under way.
The €2bn development, one of the biggest ever in Dublin, will also see the building of a new town centre as well as retail and office space.
The development is supported by Dún Laoghaire-Rathdown County Council and will take ten years to complete.
The 157 hectare (388-acre) site has Strategic Development Zone status and the masterplan has been approved by An Bord Pleanála.
Developers need only apply to the council for subsequent planning permission which must be granted as long as it is in accordance with the masterplan.
No third parties such as neighbours may object.
The development is on the site of an old settlement, with several monuments there dating from the 12th Century. They include Tully Church, an adjoining graveyard, and two high crosses.
One of the crosses bears the image of Saint Laurence O'Toole, Archbishop of Dublin at the time of the Norman invasion of Ireland.
A 22-acre park will be built around the monuments.
Dún Laoghaire-Rathdown County Council says it will consult with the Office of Public Works regarding further protective measures on completion.
