Half of those arriving in six countries were Syrians fleeing war and the overwhelming majority landed in Greece.
In the hot, grimy Balkan summer of 2015, hundreds of thousands made their way north.
Men, women and children walked countless kilometres and slept in ditches or makeshift camps, depending on the hospitality of strangers for shelter and water.
They were refugees from Syria, Iraq, Afghanistan and many other countries.
I first met Hussein Rassim in one such camp, at Presevo in Serbia.
It was a little border town, the streets littered with the debris of travellers passing through.
“Hey! They’re not feeding these guys,” he said, interrupting a conversation I was having with a Red Cross worker.
“They’re only feeding the children. There’s nothing for adults,” the young man told me in American-accented English.
He was hungry, but could not leave the camp to buy food.
If he did that, he would have to queue for hours in the 35C heat to re-enter.
We talked, then I interviewed him for a TV report we were making that night.
I asked the classic questions.
Where are you from?
Why did you leave?
“Daesh are threatening everyone.”
Where do you want to go?
“To Brussels, to make music. I play the oud. You know, the lute.”
It was one of hundreds of encounters I’ve had with refugees this year.
I had no idea how much it would affect me. I had no idea how that chance meeting would affect him too.
Hussein and I became friends on Facebook.
We thought we would meet up again on the road. Maybe in Belgrade. Or in Budapest, where he slept in the street.
I was delighted to see him posting a picture of himself in Brussels’ famous Grande Place 10 days later.
He was wandering among the tourists, his face cracked by a huge smile. He had made it.
But the refugee story is never so simple. Hussein was safe, he had shelter. But the personal isolation and dislocation for all refugees is huge.
It became clear to me that Hussein would be no different. He would face the challenges anyone faces when they are separated from friends, family and their whole culture.
One day he posted an old picture of himself on Facebook, cradling the lute he had left behind in Iraq. He was looking relaxed, eating a quick meal between playing his music.
Yet, his actual post was laced with sadness. He missed his music. He felt a little adrift. But I thought that I could do something about it.
I mentioned Hussein to a friend who lives in Brussels, I thought she might know a musician who could help him out. But Maeve was far more ambitious.
“We can crowd-fund him. We can ask all of our friends to pay a little to buy him a new lute.”
I had so many worries about it. For example, the money for one lute could feed many people. But Maeve’s enthusiasm carried the day.
The lute was found, dozens of people contributed in the online campaign and the instrument was bought.
A beautiful golden-coloured thing, fashioned from ancient wood.
The joy it brought to Hussein taught me a huge lesson.
A chance meeting became a friendship that would not have happened without social media.
The campaign to buy the lute would never have been possible without this technology. And the wave of sympathy for refugees pouring from the caring people of Europe was happening on Twitter, Facebook and other outlets.
My hope was that Hussein would get some consolation. But it has given him more. He was asked to play in a group of fellow refugees and work on an album of songs.
Now I am sitting in a theatre in Brussels, watching him play his beautiful music with a group of other refugee musicians.
If you want to buy the CD, the wonder of social media will let you help to fund it. Just search “Refugees for Refugees” and “MuziekPublique”.
The experience taught me that we are all intimately connected and that a small display of emotion can now make an impact, even in vast movements such as the summer flood of refugees.
When governments wilfully fail, a little human understanding can allow any person to show what they are truly capable of.
That might be a barber from Aleppo, an engineer from Kabul or a musician from Diyala.