Ten years ago Germans were putting balloons on lampposts to greet a multitude of foreigners. The popular tabloid, Bild, screamed the headline 'Refugees Welcome' as a million or more migrants began to flow over the border.

Warehouses in Berlin were stacked high with donated clothes, food parcels and toys for the new arrivals. Camp beds to house the guests filled sports halls, while housewives, business owners, students and social workers volunteered to help in a nation still compensating for its Nazi past.

On August 25, 2015, Germany's immigration ministry announced that Syrians fleeing civil war would be waved in with few checks or questions. Then came the moment that changed Europe for ever.

On August 31, Chancellor Angela Merkel uttered her now infamous rallying cry at a Press conference. 'Wir Schaffen Das' or 'We can do it.'

Her words were a clarion call to people the world over to come to her country, sparking an immigration crisis with all and sundry from a myriad of nations heading to Germany.

It was an uncontrolled diaspora with repercussions that are still rocking the EU bloc of 450 million people, as well as Britain – as the huge number of anti-immigration protests planned across the UK this weekend demonstrate only too clearly.

I had a frontline seat watching those tumultuous times. I walked into Berlin with some of the first Syrians to reach the city after Mrs Merkel made her speech. They were four young men from the capital Damascus who were billeted in a sports hall and dreamed of becoming engineers at BMW car factories.

A few days later, I witnessed the Merkel trains rumble into provincial towns where they disgorged the incomers – not only Syrians, but people of every nationality.

Those fleeing African dictatorships, the ISIS badlands of the Middle East, Muslim Balkan communities and huge numbers of opportunist economic migrants – all joined the caravan.

In one town I saw Roma men get off the trains and start playing their stringed instrument, the cimbalom, before begging for money from Germans eating breakfast in cafes.

In Giessen, just after Merkel's speech, I met three Pakistani men who had given up good airport jobs in Karachi to claim asylum in Germany. With their wives and children, they had been given a five-bedroom house.

'Thank God for Mrs Merkel,' said Arif, 34, the head of the family unit when I found him in a curry restaurant. 'We were fed up with Pakistan.'

Much of Europe followed Germany's lead, letting in any migrants who knocked. Throngs heading for Germany were helped on sea journeys into Europe by Italy, Spain and Greece.

Parts of Scandinavia, keen to copy Germany's largesse, became an open house for those who didn't fancy life in Berlin or Hamburg. Liberal Sweden emptied holiday camps for those who arrived.

There, Iraqi children – many of them teenage boys – were put in youth hostels. They told me they used state bank cards to access spending money from ATMs. I followed them there to see if this could possibly be true. It was.

One icy morning as the autumn drew on, I felt a sense of foreboding as I watched huge groups of young male migrants standing idly by in Sweden's second city Malmo. They looked on dispassionately while Swedes trudged to work in stout boots through the snow.

In Italy, it was the same tale. Plucked from flimsy traffickers' boats off Sicily by Italian Navy warships, migrants were soon walking down gangplanks at ports to be greeted by charity workers clapping and the locals singing Italy's national anthem.

Spanish coastguards were brought back from retirement to search the coast off Costa Blanca's beaches to scoop up migrants sailing to Europe from the north African coast. 

One evening in Alicante, as yet another coastguard boat carrying them headed for shore, I heard a group of schoolboys remarking ruefully: 'The Moors are invading us again.' They knew the history of the sixth-century Muslim conquest of their region.

On Greek island Kos, I chatted at a refugee shelter to Syrian sons of wealthy army officers who had arrived from Izmir in Turkey by traffickers' boat. They had joined the throngs to avoid conscription into Assad's army fighting a civil war against ISIS.

One of these princelings said to me, in perfect English learned at private school, 'I never thought I would have to travel with slaves,' as he pointed to two Somalian ladies who had arrived on the same boat as him.

At the same shelter, sharp-tongued, hijab-wearing Arab wives were telling Greek refugee workers that they had human rights.

The women complained the chicken and rice being served by volunteers was without spices. They demanded that the Greek authorities send them and their families to Athens so they could make their way quickly to Germany.

Days later, I watched in disbelief when the Kos migrants were put on ferries to the mainland, before marching to the Croatian capital Zagreb.

Some pinned a picture of Merkel to trees in Zagreb's main avenue as they waited. Others sported red wristbands with the word Germany on them and waved them at the Mail's photographers.

Ahead of them on their journey to Mrs Merkel's promised land was Slovenia, which sent riot police to its border with Croatia to stop the now increasingly demanding migrants flowing through from Zagreb.

I sat in a car one evening as a Slovenian riot police officer, whom I had spoken to earlier, gave me a Churchillian victory sign before holding up his shield as 700 marched towards him at a border post. An hour later, he and the police were overwhelmed by the sheer numbers and on they went towards Berlin.

Meanwhile, an EU emergency report had warned before Mrs Merkel's speech that only a fifth of those massing at European borders were genuine Syrian refugees. Many, it predicted, were lying about their nationality to get a foothold in Europe.

Despite this, a poorly worded announcement was put out publicly, via Twitter, by the German Office Of Migration, at 1.30pm on Thursday, August 25, 2015, which read: 'For the most part border controls are not being implemented by us.'

Marked as Instruction 93605/Syria/2015, it was only meant to relate to Syrians but sparked a free-for-all because it could be read by anyone, anywhere, who had half a mind to head for Germany.

'That tweet was a big mistake,' commented a member of Mrs Merkel's staff afterwards. 'We were rubbing our eyes in disbelief,' added another whistleblower at the migration office itself.

The leader of one EU country on the migrant route to Germany pointed out: 'This message is an invitation to the refugees in camps in Turkey, Lebanon and Jordan [to start their journey to Europe]. It has spread like wildfire on social media.'

As the crisis unfolded, an emergency meeting of ministers was called on the eighth floor of Mrs Merkel's private offices. German MPs asked their Chancellor, sarcastically, whom she imagined might enter the country next? 

'Even the North Koreans?' said one bravely to her face. Oblivious to the gallows humour, she responded: 'But they can't get out of North Korea.'

By the time Mrs Merkel made her famous 'Wir Schaffen Das' speech, nearly 11,000 migrants a day were pouring into German cities such as Munich, a situation that border police said was 'catastrophic'.

The numbers continued to soar. Germany took in 1.1 million migrants and asylum seekers in 2015, more than any other European country in the same period.

The question is why did Merkel do it? There's no doubt that, given Germany's dark past, she was afraid of damaging images showing desperate women and child 'refugees' crying for sanctuary at her border. 

Yet, I am convinced the migration crisis stalking Europe and Britain today was also provoked by her own hubris.

Angela Merkel, I am told, believed her welcome to Syrians would win her a place in the history books, even bring a Nobel Peace Prize. 

Warned by one of her ministers to 'save Europe' by halting what had become the 'refugee tourism' she had enabled, her response was revealing: 'You will see, in ten years' time, what I do now will be considered historical.' Indeed it is. 

Soon after the borders were opened, a poll revealed 43 per cent of Germans believed immigration was too high – even though it was just getting going.

Outside a new refugee house for 80 migrants in the Saxony town of Heidenau, the first public revolt against Mrs Merkel came the very week her speech was made.

Locals, egged on by far Right activists, threw smoke bombs and shouted racist slogans at the migrants inside. Merkel tried to pacify the town by making a personal visit. 

As she stepped out of her bomb-proof car, surrounded by security guards, the booing started. 'Get back into your ugly car,' shouted one woman as others chanted: 'Nein, Nein, Nein.'

Another woman yelled: 'Traitor to the people.' Mrs Merkel was rushed in to greet the migrants before being hurried to her limousine and driven back to Berlin. As one of her staff said afterwards: 'She expected a warm welcome. She was wanting applause,' explaining that the Chancellor was very surprised at not getting it.

Last week, I went to Heidenau where the refugee house was closed ten weeks after the riot. People there remember vividly the day the Chancellor was run out of town. 'She didn't stay long, did she?' observed one resident in his 70s, walking his dog near the former refugee house.

I also went to the same Berlin street where, in September 2015, I met those young Syrians arriving in Germany for a new life.

One of them, 25-year-old Mohammad Abaan, warned me of the disaster unfolding. He banged his hand on our cafe table and declared: 'Every day more Africans, Afghanis, Iraqis, Palestinians, Lebanese, Egyptians, Tunisians and all sorts of Roma people slip into Germany through a door opened by Mrs Merkel for us Syrians.' 

He pointed out foreign men walking past in Islamic robes. 'They travelled with us, they are staying with us, but they are Somalians,' he explained. 'They pretend to be from Damascus, but they are lying. Their skin is blacker and they have different beard cuts to us. Germany is being deceived.'

I reported his words in a dispatch to the Mail. But Mohammed went further. He drew a pie chart in my notebook to show that he believed two in three migrants were fraudulently posing as Syrians (a higher proportion than even the EU estimated at the time).

I am convinced now that a great migration scam was played on Germany, facilitated by a liberal-minded Chancellor trying to amend for her country's ugly past.

There may have been another reason for Mrs Merkel's refusal to shut her borders to a mainly Muslim contingent of migrants entering a Christian country.

A few months before her, 'We can do it' speech, she declared 'Islam is part of Germany', in a statement that made headlines.

It coincided with the attack on satirical magazine Charlie Hebdo in Paris. It had published satirical images of the prophet Muhammad in 2015 and was targeted by two French-born Algerian terrorists who shot dead 12 people including five of its cartoonists.

Following the massacre, Mrs Merkel attended a Hebdo vigil in Berlin. There, she was photographed linking arms with Aiman Mazyek, then secretary general of Germany's influential Central Council of Muslims.

At the event, she went on to rail against the dangers of Islamophobia. I was shown the picture this week by Alice Schwarzer, one of Germany's most famous journalists and old-style feminists, who has led the debate on Islam, the burka and mass migration's impact on German women.

Ms Schwarzer, once a friend of Mrs Merkel, said: 'Her welcome to Muslim migrants in 2015 was not out of ignorance.'

She believes Mrs Merkel was heavily influenced by Islam 'ideology' which became more important to her than 'reality'.

Whatever the truth, the consequences of Mrs Merkel's actions are still being felt in Germany, not least politically as the country swings dramatically to the Right.

When I walked into Berlin with the first Syrians, a tiny political group, Alternative For Germany (AFD), had just been set up. It was polling at three per cent on a manifesto of closing the borders and the dire warning that German's economic miracle would disappear with so many foreign migrants to feed and clothe.

This month, a new poll showed that 26 per cent of Germans would now vote for the AFD as it overtook the ruling conservative bloc in popularity.

Few know what Mrs Merkel thinks in her retirement of this earthquake. Meanwhile Germany, the rest of Europe and we in Britain must confront the weight of mass migration – as she remains resolutely silent.