Barriers, sandbags and concrete lions are among the preventive measures deployed in European city centres in the wake of a spate of vehicular terror attacks across the continent over the past year.

Following two such attacks in Barcelona and the nearby resort of Cambrils, experts cautioned that their low-tech nature and soft targets make them impossible to prevent altogether.

But in many countries roadside obstacles and beefed-up policing in crowded areas and city landmarks are seen as a way of reducing the risk.

Here are some examples:

LONDON: Security barriers were hastily put up along the pavements on three bridges in central London in June, days after three attackers wearing fake suicide vests in a van struck pedestrians on London Bridge

Eight people were killed in that attack, which came after a similar one in March in which a man in his car mowed down people on Westminster Bridge before stabbing to death an unarmed policeman who was guarding parliament.

Similar measures had already been taken outside royal palaces following the Berlin Christmas market vehicle attack in December 2016 in which 12 people were killed.

Roads in front of Buckingham Palace are now closed off during the Changing of the Guard military ceremony, which regularly draws tourist crowds.

Concrete barriers were also installed outside Windsor Palace, the queen's residence outside London.

Barriers have been in place outside parliament and government buildings for years.

FRANCE: There have been several attacks using vehicles in France since a man rammed a truck into a crowd in the Mediterranean resort of Nice on July 14, 2016, killing 86 people and injuring 400.

Temporary concrete barriers are now regularly set up outside "large gatherings", for example, on the famous Champs Elysees avenue in Paris and in the historic centre of Strasbourg, French police said.

Along the pedestrianised banks of the River Seine in Paris, car access in some points is possible to allow emergency vehicles to get through but these are now blocked by police cars when not in use.

BERLIN: Security measures have been more limited in Germany despite the Berlin Christmas market attack.

Concrete barriers were installed in front of some markets at the time but have since been taken away.

Following Thursday's attacks in Spain, Lorenz Caffier, interior minister in the northeastern state of Mecklenburg-Western Pomerania, said more barriers should be set up to protect pedestrianised areas.

But he admitted that it was "almost impossible" to prevent this kind of attack.

Concrete blocks were also set up at some major Christmas markets in Austria after the Berlin attack.

But "excluding risk is an illusion," interior ministry spokesman Karl-Heinz Grunboeck told AFP.

"It is impossible to separate pedestrians and cars to completely exclude the possibility of an attack. We can only reduce the risks," he said.  

BRUSSELS: Belgian security officials said they have recommended setting up concrete barriers and other measures to protect soft targets like large concentrations of people, especially since the November 13, 2015, terror attacks in Paris.

A police spokesman said sandbags weighing one tonne each and concrete blocks are among the preventive measures in the city, which was struck by three coordinated suicide bombings on March 22, 2016.

STOCKHOLM: Barriers in the shape of concrete lions were set up on the Swedish capital's main pedestrianised streets after a truck struck shoppers outside a busy department store in April, killing five people including an 11-year-old girl.

The attack happened on Stockholm's busiest shopping street Drottninggatan, where local authorities have also now installed some granite blocks.

The city has also ordered 40 new concrete lions that will be heavier -- weighing three tonnes compared with 900 kilograms for the current ones.