The opening of the first high-speed road link between Belfast and Dublin has been hailed as a boost to Ireland, north and south.
Taoiseach Brian Cowen, and Northern Ireland Deputy First Minister Martin McGuinness led ministers at the ceremony at Newry, Co Down, to open the multi-million pound route.
Both leaders hailed the development as proof that cross-border co-operation can help replace the era of the Troubles with a more prosperous future.
The completion of the link cuts the travel time between the two cities to under two hours.
"It brings all of us closer," said Mr Cowen, who added that the development would bring economic and social benefits.
Sinn Fein's Regional Development Minister Conor Murphy, accompanied by DUP junior minister Robin Newton, said the final 7.5-mile (12km) phase of the route was completed five months ahead of schedule and cost 179 euro (£150 million).