If the rise of militant anti-clericalism in Britain is a relatively new phenomenon for a Pope to witness, a more familiar foe was holding court little more than half a mile away in the Grassmarket.
The Reverend Ian Paisley protested at the visit of Benedict's predecessor, John Paul II, and despite his advancing years, he was not prepared to miss out on this occasion.
The former First Minister, now 84, spent 90 minutes with around 50 elders from the Free Presbyterian Church at the Magdalen Chapel in the Cowgate, having arrived that morning from Northern Ireland.
The location was appropriately bathed in anti-Rome symbolism: built in 1541, it was the last church to be constructed in Edinburgh before the Reformation and provided the setting for the first meeting of the Church of Scotland attended by John Knox.
Members of the Free Presbyterian Church unveiled a banner near the Magdalen Chapel and distributed booklets outlining their opposition to the Pope's trip.
The booklet stated that "recent scandals" within the Roman Catholic Church meant that the Pope would not receive a universal welcome.
A black-hatted Dr Paisley, now Lord Bannside, emerged from the ancient stone doorway to remind the large contingent of gathered media that he was not here to receive the Pope's blessing. "I will be keeping as far away as possible because the whole thing is nonsense," he said.
The Ulstermen then paraded a short walk up to the cobbled streets to gather at the Martyrs' Monument, where evangelical Protestants were put to death more than 400 years ago, to hold a short religious service in the open air.
Dr Paisley told those gathered: "We're here today on very solemn and serious matters. I've just seen the statement that has been issued by the Roman Catholic Church about this visit and we are told that if we go to this mass here today then we will have a shortened purgatory and our sins will be forgiven - £25 and you'll get out of purgatory quicker.
"Now there's no such a place as purgatory, so that's a farce from the very beginning. Secondly, no man can forgive sins but God only."
He added: "I believe in gospel without money and without price."
True to his word, Dr Paisley then turned his back on the Pope and set off in the opposite direction.
Meanwhile Pope Benedict's determination to confront Britain's "aggressive secularism" was put to an early test – but the anti-religious forces which gathered to greet him on the streets of Edinburgh were quite a jolly lot even if their message was a deadly serious one.
The hooters began to sound as soon as the pontiff's motorcade turned off Princes Street and made its stately way down Lothian Road, where opponents of the visit were staging their demonstrations. Lines of police officers stretched in every direction, while a sinister-looking white eyeball attached to the roof of the lead vehicle filmed the 200 or so protesters lustily booing Benedict for all they were worth.
From behind the bulletproof glass of his Popemobile, the pontiff seemed completely unfazed by his reception, briefly looking away before waving and smiling serenely at his detractors as they brandished placards urging "Justice for the Abused", "Condoms Save Lives" and "Nope to the Pope". Perhaps he simply couldn't hear them.
"He looks like a kindly old man, but I am sure Hitler could be perfectly charming at times, too," said Anne Hay, 57, an adult literacy teacher who was on her first demonstration. "I believe in liberal values and the Pope stands for everything that is against those values – rights for women, allowing them to have control over their own bodies, and rights for gay people – and that is before you even start on the paedophile issue," she said.
Mirjam Urfer, 34, a Swiss-born interpreter, was handing out free condoms to passers-by to show her disdain for the Pope's conservative views on contraception. Having been brought up a Catholic she had since "deconverted" to humanism. "My Catholic education was an indoctrination. A fear was implanted in my brain which prevented me from living a happy life for a long time," she said.
Mike Williamson, 21, a student at Edinburgh University who organised the protest, said he too had rejected his faith after becoming disillusioned during a teenage pilgrimage to Lourdes. He was worried about why the cost of policing the visit was coming out of budgets at a time when officers were facing redundancy. "We wanted to send a message to the Government that the public is not happy with him being given a state visit," he said.