It was not the most conventional way for a Government leader to greet Europe's chief bureaucrat. But then these aren't ordinary times as regards Ireland and the European Union.
"Romano, how are we doin'?" Mr Ahern bellowed from the steps of Government Buildings as a startled-looking Mr Prodi emerged from his chauffeur-driven Merc. Hugs and handshakes, smiles and back-slaps followed. But nothing could hide the tension in the air.
Just a few steps away, journalists were being told "absolutely no questions" - not, at least, until the two leaders had time to meet, and presumably get onto the same hymn sheet regarding the Nice Treaty and the need for it. Cameramen wishing to follow the two inside were ordered to remove all microphones.
One couldn't blame Mr Prodi for feeling a little anxious. He had, after all, just landed his host in the political soup by declaring ahead of his visit that enlargement could go ahead without ratification of the treaty, contrary to what the Government argued in the referendum campaign.
His comments had raised eyebrows in European quarters too. Questions were again being asked about Mr Prodi's suitability as president of the Commission.
It was all very different to the visit he no doubt had planned. Had the treaty referendum succeeded, as expected, his four days in Ireland would have passed without much attention. A few complimentary remarks about Ireland being the head boy of Europe would no doubt have been delivered ahead of a leisurely spin round the Ring of Kerry with Commissioner David Byrne, et al.
Instead, Mr Prodi found his himself door-stepped at every turn by a media, which for once couldn't get enough of "Europe". His comments on Nice, "the Irish problem" and the future of the Union were analysed.
Worse, the Commission president faced the indignity of having to meet some key figures of the No campaign, Europhobes - as they would be labelled in Brussels - who are threatening to scupper his vision for an enlarged and more integrated Union.
Mr Prodi endured it all gracefully, however, as well he might. Despite all his talk of being here to listen rather than speak, there was an undoubted element of the soft sell to his visit. Or rather, a re-selling of Europe.
Not that Mr Prodi was the only peace emissary to arrive from the mainland. The president of the European Central Bank, Mr Wim Duisenberg, swung into town on a more overt public relations exercise. Expressing his "personal" regret about Ireland's No vote, he came to Dublin Castle with his powerful governing council to remind us of what we have already got ourselves into.
While both visits were planned months ago, or so the two Euro heavyweights' handlers would have us believe, their timing could not have been better. As well as focusing minds on our relationship with the EU as we face a renewed debate on Nice, they allowed us to see exactly what these Eurocrats, that junior minister Eamon O Cuiv complains about, are like in the flesh.
In the case of Mr Duisenberg, a chain-smoking golf enthusiast who is known to like a tipple - frankly, he didn't seem all that different to one of us. That, at any rate, was the message he appeared to try to get across.
Challenging the "us and them" mentality which threatens to undermine European cohesion, he urged people to see the euro as "our money" and the ECB as "our central bank". "Our currency," he said, used by "our population" will make "our lives easier".
That was Wednesday afternoon when Mr Duisenberg - or "President Duisenberg" as the Central Bank of Ireland governor Mr Maurice O'Connell likes to call him - was addressing a euro information forum at the Bank of Ireland Arts Centre. By Thursday the action had moved to Dublin Castle for the main purpose of his trip, a meeting of the ECB governing council - only the third to take place outside of Frankfurt in the bank's 30-month history.
The idea was to counteract the impression of a Europe "over there" by bringing the governors of the 12 eurozone states and the council's six executive members here for one of their important fortnightly meetings. Depending on one's view, this was a shining example of the Union in action or a salient reminder of how much power we have already ceded to Europe.
With the establishment of the euro on January 1st, 1999, Irish monetary policy effectively ceased to exist, with the ECB assuming responsibility for interest rates. Not only that but Ireland is now not even allowed to make a case for a change in policy that would suit our national interests.
"Our governor does not represent Ireland in there. Legally, he is not allowed to," said Central Bank of Ireland spokesman Mr Neil Whoriskey. "Everything is done on a euro area basis and he has to decide on what's best for all euro countries. He can't put his hand up and say `actually, we'd like higher, not lower, interest rates' just because it would suit us better."
It would suit us better for the ECB to raise rates. But the governing council, in its wisdom, decided against it. For half an hour after the meeting, Mr Duisenberg - a man described by the Economist as a "famously dull speaker" - fielded questions from the press about the (non-)decision and then he was on his way.
Here, was the EU in all its monotonous glory. Fittingly, Dublin got to see it on the longest day of the year, the summer solstice. Ten minutes of the ECB president talking about the "two pillars" of monetary policy strategy felt like an eternity to the uninitiated.
In the context of the current row over Europe, however, Mr Duisenberg's job was patently not as tricky as Mr Prodi's. Where the ECB president was simply reminding us of our existing commitments, the Commission president was contemplating future ones. And by yesterday afternoon, the Italian was showing signs of strain.
"This is not a gaffe," he cried, his voice straining with anger. What he had said to The Irish Times this week, he had said before - namely that the Nice treaty was a political but not a legal requirement for enlargement - "this is the truth."
His comments were addressed to a crowded press conference in the Commission's Irish office, just an hour after meeting a group of No campaigning MEPs and activists. He said the meeting was an attempt to understand and "have a dialogue", although those on the other side of the table saw it differently.
"For a listening exercise, he did quite a lot of talking - more talking than any of the people he was supposed to be listening to," said one of the No delegation afterwards. "He was quite dismissive really. He was just going through the motions."
For all that, the No camp was chuffed to have commanded his attention and lost no time in using him - and his comments - as a stick with which to beat the Government. "By virtue of him meeting us he has shown how unreasonable the Government has been," said Mr Justin Barrett of the No to Nice Campaign.
"I wish we had more politicians like Mr Prodi," said Dana Rosemary Scallon. "He just tells the truth."
The Commission president could probably have done without compliments like these. Eager not be colonised by the No camp, he assured the media "the Irish Government did not lie" to the electorate. Then, growing more exasperated, he declared: "You have the right to make any confusion", his command of the English language slipping for once.
Criticism of his suggestion that a euro tax be introduced also got his back up. He was not, he stressed, recommending higher taxation. Nowhere in Europe was there misunderstanding of his views, he said, "except here".
One got the feeling that while he "welcomed" the debate on Europe that had begun, he'd rather he wasn't here for it, especially while it was in its infancy.
One got the feeling too that tomorrow, when he gets back to Brussels, he will be giving the Commission a very different report to that expected when he left.
It's official, he might well conclude, Europe's head boy has rebelled.