Paris - With Poland starting work on a 353-million-euro ($407 million) wall along its frontier with Belarus, we look at other border barriers that have sprung up across Europe, particularly since the migrant crisis of 2015.

- Greek-Turkish border -

In 2012, Greece built two three-metre tall barbed wire barriers along 11 kilometres (seven miles) of its frontier with Turkey, which has previously been mined.

Greece became the main point of entry into the European Union for migrants when its economy collapsed after the financial crisis of 2009. Many crossed the River Evros, which forms a natural barrier along much of the 150-kilometre-long border.

In 2020, after Turkey "opened the doors" for migrants to enter the EU, Athens begins building an "impenetrable" 40-kilometre (25-mile) extension to the barrier, which was completed in August.

Greek soldiers also guard a one-kilometre-deep military zone along the border, interspersed with towers and surveillance equipment.

Graphic of the barrier Poland is building along its border with Belarus

- Bulgarian-Turkish border -

In 2014 Bulgaria put up a 30-kilometre barbed wire fence along its border with Turkey as migrants flock there to avoid the perilous Mediterranean Sea crossing.

Four years later the fence is extended to cover almost all of the 259-kilometre border.

Map of border walls in Europe

- Hungary-Serbia, Hungary-Croatia barriers -

During the 2015 migrant crisis, as more than a million people fleeing wars and poverty try to reach Europe, barriers spring up across the Balkan route to stop them.

Hungary's populist government, led by Viktor Orban, throws up a four-metre, 175-kilometre barbed wire fence along the frontier with Serbia before building another, 120 kilometres long, along Hungary's border with Croatia.

- Slovenia-Croatia border -

In the weeks that followed, Slovenia closed off nearly a third of its 640-kilometre border with Croatia with barbed wire. It has since built a fence along parts of the route near towns and tourist areas.

-  Greek-North Macedonia border -

In November 2015, with thousands of migrants crossing its southern border through fields around Gevgelija, Skopje built a three-kilometre metal barrier to slow them. Another followed further to the west near Medzitlija and a third near Lake Dojran in the south east. Between them they now cover more than 32 kilometres.

- Austria-Slovenian border -

Austria put up an anti-migrant barrier on part of its border with Slovenia in December 2015, the first within the Schengen area, where they are no passport checks.

Another smaller one follows on the Brenner Pass with Italy. Both have since become overgrown with vegetation and breached with gaps for walkers, wildlife and local farmers.

- France's Calais fences -

France built about a dozen kilometres of formidable "anti-intrusion" walls and fences around its northern port of Calais and the entrance to the Channel Tunnel to stop migrants crossing to Britain.

Most migrants now try to cross the Channel in small boats, with a record 1,185 attempting the crossing one day in November 2021.

- Spain: Ceuta and Melilla -

The Spanish enclaves of Ceuta and Melilla on the northern Moroccan coast are Europe's only land border with Africa. Both are surrounded by kilometres of fences and barbed wire, with charities repeatedly criticising the use of razor wire around Melilla.

Factfile on the Spanish enclaves of Ceuta and Mellila

By Florence De Marignan