Nearly 1 million migrants, many of them refugees from Middle Eastern war zones, reached Europe by crossing the Mediterranean Sea in the first 11 months of 2015.
But, whereas most migrants arrived across the central Mediterranean route in 2014, the surge shifted eastward in 2015, leading people to take the Balkan route. Additionally, the number of arrivals started to rise dramatically in April.
By September, the numbers had inflated so much that the first eight months of 2015 saw three times more migrants trying the Balkan route than the combined figures for people who attempted the route in 2013 (19,500) and 2014 (43,300).
Of the 925,000 people who came by December 12, according to the International Organization for Migration, 771,500 took that path, from Turkey to Greece. Of the 3,600 who drowned in the sea, 684 perished between Turkey and Greek Aegean islands.
Below is a chronology of key events on the Balkan route:
A wave of economic migrants, mostly Kosovo Albanians, illegally entering Western Europe abates after three months.
- Migrants, mostly refugees from Syria, begin arriving at a dramatically increasing pace. Large groups make progress by walking along the highways and railroads of Greece, Macedonia, Serbia and Hungary.
23 - EU leaders pledge to triple funding for Mediterranean Sea patrols after more than 800 migrants are estimated to have died in a shipwreck off the coast of Libya.
24 - Train kills 14 migrants walking along the railway in a Macedonian gorge. A day later another migrant is killed on the same railway.
The EU launches a military mission in the Mediterranean Sea aimed at cracking down on migrant smuggling networks.
EU interior ministers agree to redistribute 40,000 asylum seekers from Greece and Italy to other EU countries and resettle 20,000 refugees from outside the bloc.
22 - Migrants clash with Macedonian police blocking their entry from Greece. Police eventually withdraw, allowing thousands through. Macedonian authorities deploy additional trains to shuttle people to the border with Serbia.
27 - A truck with the bodies of 71 migrants, most of them Iraqis, is found in Austria. They suffocated in the refrigerated cargo area during a trip organized by people smugglers.
2 - Aylan Kurdi, a 3-year-old Syrian whose family tried to reach Europe from Turkey, dies. Their dinghy capsized and Aylan drowned, as did his mother and brother. Photos of his body washed ashore shock the world and riveted its attention to refugees.
3 - Hungary's conservative Prime Minister Viktor Orban says that his country does not want to receive Muslim refugees.
15 - Hungary completes a fence along the 177-kilometre frontier with Serbia and seals its border to migrants. The flow is diverted to Croatia. After a few days of adjusting, Croatia channels the people to Hungary.
22 - EU interior ministers agree to redistribute a total of 160,000 asylum seekers from Greece, Italy and other migration frontline states to other EU countries. They outvote the Czech Republic, Hungary, Romania and Slovakia in the process. Slovakia and Hungary challenge the decision in EU courts.
17 - Hungary stops admitting migrants from Croatia, too, after constructing a fence along parts of the border. The flow is now diverted to Slovenia, which becomes the new and the smallest country on the main Balkan route. Over the subsequent six weeks, Slovenia channels more than 277,000 migrants across its territory.
21- EU and Balkan leaders agree to cooperate in limiting the uncontrolled tide of migrants and asylum seekers flowing through their territories.
3 - Migrants are transported by ferry, train and bus directly between reception centres in Macedonia, Serbia, Croatia and Slovenia, which spares them waiting at the borders in deteriorating weather and perils of trekking.
11 - Slovenia begins building a fence along its border with Croatia to put the inflow of migrants under control.
12 - The EU launches a 1.9-billion-euro fund to tackle migration from Africa and seeks to secure the cooperation of African partners at a summit in Malta to control migration flows.
16 - Macedonia begins preparing ground for fence along the border with Greece to control migration flow, starts erecting it 12 days later.
20 - Slovenia, Croatia, Serbia and Macedonia stop economic migrants and begin allowing only refugees from Syria, Iraq and Afghanistan to enter. A crowd of mostly Iranians, Pakistanis, Bangladeshis and Moroccans builds at the Greece-Macedonia border.
29 - The EU strikes a deal with Turkey to offer refugee aid and boost relations with Ankara in return for efforts to curb migration flows into the bloc.
7 - Austria begins building a 4-kilometre, 2.2-metre tall fence along the border with Slovenia to channel the flow of migrants.
9 - Greece clears some 2,000 economic migrants - from Iran, Pakistan, Bangladesh, Morocco and elsewhere - from the border with Macedonia and takes them to Athens without a clear plan what to do with them. Most refuse to return home.
15 - EU border-managing agency FRONTEX says monthly migrant influx declined in November, the first time that happened in 2015. Still, the 667,000 registered arrivals on the Balkan route marked a more than 20-fold increase from the previous year.