Police have placed barriers in front the Cologne Cathedral. The measure follows reports that militants sought to target Barcelona's Sagrada Familia - another, albeit more modern, icon of ecclesiastical architecture.
"We took the decision to act as quickly as possible after looking at attacks in Europe," a spokeswoman for the police department said on Wednesday. "Our job is to protect sensitive spots - and the cathedral is a symbol of Cologne, known around the world."
Large stone blocks will form a barrier at the entrance to the public square in front of the cathedral.
Hit 14 times by Allied bombs during World War II, Cologne's cathedral survived structurally and reopened after repairs in 1956. In 1996, UNESCO added it to its World Heritage List.
World Heritage Site: Cologne Cathedral
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'Calm and relaxedness'
Media reported that the militant cell in Catalonia had also plotted an attack on Antoni Gaudi's Gothic-Art Nouveau hybrid Sagrada Familia church. Although militants have employed automobiles in a handful of attacks in Europe over the past year, many cities - deterred by high costs, the temporary nature of such measures and a reluctance to disrupt everyday life - have not rushed to mitigate risks by changing their layouts.
"We don't want to wall up the city," Andreas Geisel, Berlin's city-state interior minister, said in an interview with Bild newspaper published on Wednesday. "That would achieve the opposite of what we want: to send out an image of calm and relaxedness."
Though Germany's capital has implemented few other measures, barriers remain in place around the site of a Christmas market where a militant drove a stolen truck into crowds and killed 12 people last year. Berlin's Protestant cathedral will also continue to maintain increased security measures, including bag checks and regular preparedness drills, implemented following a series of terror attacks in Paris in November 2015.
Spain terror attacks - what we know
Twin vehicle attacks in the Spanish cities of Barcelona and Cambrils have left 14 people dead and more than 120 injured. Police have arrested four men and are searching for other suspects believed to be on the run.
Image: picture-alliance/AP Photo/O. Duran
Terror attack
Witnesses in Barcelona said a van zigzagged down one of city's busiest tourist avenues, Las Ramblas, mowing down pedestrians and leaving bodies strewn across the ground. Police confirmed it was a terrorist attack.
Image: Getty Images/AFP/J. Lago
Second rampage
Several hours later, a speeding car killed one person and injured five in the seaside resort of Cambrils. The car's five occupants were shot dead by police. Catalonian authorities have confirmed that the two attacks were linked.
Image: Reuters/Reuters TV
Manhunt started
Police say they have arrested four men suspected of having a role in the attacks. They are still searching for the driver of the vehicle used in Barcelona. He is believed to be on the run, although officials have said he also could have been one of the five shot dead in Cambrils.
Image: REUTERS/Stringer
'Islamic State' claim responsibility
The so-called "Islamic State" (IS) terror group claimed responsibility for the attacks. "The perpetrators of the Barcelona attack are soldiers of the Islamic State and carried out the operation in response to calls for targeting coalition states," the group's news agency said.
Image: Getty Images/D. Ramos
Suspects in custody
Police said three of the detained suspects are Moroccan, and one is a Spaniard. None of them were known to have links to terror groups.
Image: Getty Images/AFP/J. Lago
Several victims critical
The Catalan government said that at least 13 people had died in the Barcelona attack, with 61 still receiving treatment for injuries in hospital - 17 of them in a critical condition. Four people wounded in the Cambrils attack remain in hospital. The victims came from at least 34 countries, officials said.
Image: Getty Images/AFP/J. Lago
Makeshift memorial
On Friday, thousands of people gathered around a makeshift memorial in Las Ramblas, the site where the van came to a halt. Many left flowers and candles in honor of the victims.
Image: picture alliance/ZUMAPRESS.com
Three days of mourning
Spanish Prime Minister Mariano Rajoy announced three days of official mourning for what he called a "jihadist attack." At a news conference in Barcelona, he told reporters: "Today the fight against terrorism is the principal priority for free and open societies like ours. It is a global threat and the response has to be global."
Image: Imago/robertharding/P. Higgins
Minute of silence
King Felipe of Spain, Prime Minister Rajoy and Catalonia Regional President Carles Puigdemont join crowds gathered for a minute of silence in Las Ramblas.
Image: picture alliance/AP Photo/M. Fernandez
Suspicious explosion
Spanish authorities are also investigating the scene of an explosion late Wednesday that killed one person in the city of Alcanar, some 200 kilometers (124 miles) southwest of Barcelona. Police first thought the explosion was an accident but said Thursday they now believe an explosive device intended for use in Barcelona was being prepared in the building.
Image: picture-alliance/dpa/Europa Press/Bombers De La Generalitat
