The Balkan route
As of Wednesday, the final legal door seems to have been slammed shut on the route, after Slovenia announced it would close its borders to migrants. That move was the culmination of months of ever-increasing limits on the ability of refugees to traverse the path.
Here's a look at the developments of the controls along the route amid the crisis. Note, these controls all apply to migrants: Regular travelers, especially those in possession of passports recognized by Schengen-area countries, can still travel freely.
FROM TURKEY TO GREECE:
Many refugees start the journey after they've made it to Turkey, from where they must make the dangerous water crossing of the Aegean Sea. About 850,000 made the crossing in 2015, but hundreds of others died in the attempt.
In recent weeks, Greece has opened hotspots to try to manage the flow of people onto its territory. But many migrants avoid these official sites and work their way north.
FROM GREECE TO MACEDONIA:
At least 13,000 migrants remain massed in a camp at the border town of Idomeni in Greece, with little hope of making it to Macedonia, partially due to a 30-kilometre fence laced with razor wire that Macedonia began building in November.
Officials until recently waved refugees on through to Macedonia. That changed February 18 when countries along the route - excluding Greece - agreed to only allow passage for Syrians and Iraqis, granting them a document that secured passage.
The initial control started the backup in Idomeni, which was only worsened as additional controls were implemented by successive countries. Movement came to a halt on March 9, when Slovenia, Croatia, Serbia and Macedonia said they will not allow any more migrants to pass.
FROM MACEDONIA TO SERBIA:
The border between Macedonia and Serbia, 200 kilometres north of Idomeni, remains without a fence, as only refugees with papers issued at Macedonia reach the camps in Tabanovce and in Presevo, on the Serbian side.
Police began overseeing and organizing the transport of people in the late summer. Since then, only trains and authorized buses have been allowed to shuttle migrants further.
FROM SERBIA TO HUNGARY
Initially, the preferred route for refugees took them through Hungary. That stopped when Hungarian Prime Minister Viktor Orban ordered a fence to be built along the 175-kilometre border with Serbia and sealed it in mid-September. Since then, the flow of migrants has headed through Croatia.
FROM SERBIA TO CROATIA:
Initial flows through Croatia still went through Hungary, which then erected more fencing and closed the border with its fellow EU member in mid-October.
Croatian authorities then began to shuttle the migrants out of the country onwards towards Slovenia.
FROM CROATIA TO SLOVENIA:
The smallest country on the route, Slovenia immediately began requesting countries towards the beginning of the Balkan route to stifle the flow of migrants.
In November, Ljubljana began stretching a razor-wire barrier across its entire border with Croatia, saying it wanted to channel the migrants toward controlled crossing points.
Croatia, Serbia and Macedonia followed Slovenia's lead in setting a daily cap of 500 migrants on February 25.
FROM SLOVENIA TO AUSTRIA:
Austria lets in only 80 people a day, and only those who can claim they need protection. A further 3,200 are allowed to transit the country to apply for asylum elsewhere. However, actual numbers have stayed below these quotas since they were introduced on Feburary 19.
Fences have only been built at the main border crossing with Slovenia to channel arrivals towards the checkpoint. However, there are plans to set up such controls at 12 additional crossings at the southern border with Slovenia and Italy, in case the migration flow shifts.
FROM AUSTRIA TO GERMANY:
Germany has carried out checks at its border with Austria since September. Although Berlin has never declared a quota system, the Austrian government has pointed out that German police have set hourly limits that amount to a maximum of 3,600 migrants per day.
This left up to 20,000 people temporarily stranded on the Austrian side at the peak of the migration crisis last year.