The Taoiseach yesterday launched a special commemorative 48c stamp marking the 90th anniversary of the 1916 Easter Rising.
Mr Ahern said the GPO was an iconic image in the Republic's history and represented the stage on which the key events of the Rising were played out.
"It is the most significant building, historically and architecturally, on the main street of this country's capital city," he said. "Its renewal following the devastation wreaked on it by the battle that raged during the Rising is a reflection of the renewal that has taken place in this country in the intervening years."
Mr Ahern said the modern-day GPO represented the link between a nation struggling for independence and the realisation of a sovereign independent state that today is capable of achieving its "exaltation among the nations".
The stamp, based on a contemporary photograph of the GPO by Donal Murphy, was designed by Ger Garland.