Over the summer the Schengen Agreement, which allows people to travel without showing a passport around continental Europe, has come under considerable pressure as border controls swing back into place

Happy Birthday Schengen The European Commission celebrates the 30th anniversary of the Schengen Agreement, declaring it the EU’s greatest achievement and “irreversible”

Clashes along the Italian-French border as Italian riot police attempt to stop African migrants reaching the French resort of Menton

Increased border checks Denmark announces it will increase border checks to combat crime, within the Schengen rules.

In the wake of the botched Thalys train terrorist attack, Charles Michel, the Belgian PM, calls for Schengen to be revised to allow identity checks on passengers

Merkel warns Europe to accept asylum quotas Angela Merkel warns that free movement is at risk if asylum quotas are rejected, saying: "If we don't arrive at a fair distribution, then the issue of Schengen will arise - we do not want that."

Italy tightens police checks on border with Germany, following request from state of Bavaria. "Schengen has de facto fallen apart," says Slovakian foreign minister Miroslav Lajcak

Next flashpoint in Denmark Refugees sit in a train headed to Sweden as it leaves Copenhagen Central Station (Photo: REUTERS/Linda Kastrup/Scanpix) Denmark closes a motorway and halts rail traffic north to stop movement of refugees from Germany to Sweden

Germany introduces controls at Austrian border, causing long traffic jams

Refugees queue to board a train from Budapest Keleti railway station to Munich, Germany (Photo: Rex) Hungary declares a state of emergency and seals its external Schengen border with Serbia, and closes motorway and railway into Serbia

Austria introduces controls at Hungarian border. French PM Manuel Valls says he will not hesitate to introduce border checks. Germany extends passport checks and mobile patrols to French border

Slovenia introduces controls at Hungarian border for 10 days

Refugees arrive at the Hungarian border fence Photo: AP Photo/Matthias Schrader, File Hungary begins to erect a wire fence with Croatia, a non-Schengen EU state. French Front National is accused of “provocation” after laying a wreath “in memory of free movement” at Schengen

Hungary completes its fence bordering Croatia

Sweden introduces temporary border checks Sweden becomes the latest country to introduce temporary border checks. Nearly 200,000 migrants are expected to arrive in Sweden by the end of 2015 - more per head of population than any other EU nation. "The rest of Europe has to help. We cannot be the one country, year after year, that is doing more than any other country," the country's immigration minister tells the BBC.