A couple metal beams. That’s it.

The Czech hedgehog is a simple anti-tank defense that, for Americans and Russians alike, evokes images of World War II. Allied soldiers had to navigate beaches sprinkled with them during the Normandy landings. Moscow has a monument of Czech hedgehogs to mark the furthest Nazi soldiers got to the capital city.

Black and white image of service members on a beach standing amid dozens of simple metal structures, each about 5 feet high.

In this picture taken on June 1944 on a beach in Normandy, Royal Marine commandos prepare to demolish the obstacles designed to prevent an Allied forces landing. (Photo by AFP)

Anti-tank obstacles line a snowy field in front of large buildings in the distance.

1963, Berlin Wall, border at Potsdamer Platz, anti-tank obstacle defense, Czech hedgehogs. (Photo by Sobottaullstein bild via Getty Images)

Now, Czech hedgehogs are a common sight in Ukraine as the country puts every effort into slowing down the Russian invasion. They dot the beaches of Odesa, they fill the streets of Kyiv, and they are present at key checkpoints. Many Ukrainian civilians are making them as a sort of DIY anti-tank barricade throughout their cities and towns.

An armed soldier stands guard at a roadblock.

An armed Territorial Defense soldier stands guard at a roadblock in Kyiv on Monday. (Pavlo Bagmut/Future Publishing via Getty Images)

What are Czech hedgehogs and how do they work?

Czech hedgehogs are made from two metal beams that are sealed together at angles. A third beam is added to allow the hedgehog to keep its shape and to function even when moved or tipped over. Any vehicles attempting to drive over the beams become stuck or possibly damaged — stalling the enemy from making further advancements. Such a delay makes the vehicle more vulnerable to more advanced anti-tank weapons, like shoulder-fired missiles and drones.

Anti-tank obstacles line an urban road as pedestrians walk along the sidewalk.

Czech hedgehogs on central Derybasivska Street, Odesa, southern Ukraine, on March 9. (Photo by Nina Liashonok/Ukrinform/NurPhoto via Getty Images)

When were they created?

Czech hedgehogs, also known as steel hedgehogs, have been used to protect towns and cities since their creation in Czechoslovakia in the 1930’s. Early forms of the barriers were built to defend Czechoslovakia from Germany before World War II and were then repurposed by the occupying German forces years later. They were famously part of Nazi Germany’s “Atlantic Wall,” along the French coast, in a bid to obstruct allies from landing on beaches ahead of D-Day. They were widely used by armies, including by the Soviet Union, as anti-tank defenses during the war. They’ve been used throughout the world since then.

Black-and-white image of tanks on an urban road strewn with debris.

The Nazi propaganda picture shows burned-out tanks in Kharkiv after the recapture by the German Wehrmacht in March 1943. (Photo by Berliner Verlag/Archiv/picture alliance via Getty Images)

Who is making them in Ukraine?

In short, anyone who has access to metal girders and welding equipment. Some Ukrainians are using old railroad ties to create the obstacles. In the western city of Lviv, a furniture builder began building the hedgehogs on the first day of the war. “On the first day [of the invasion], my brother came to me and said: ‘Listen, we need anti-tank obstacles,’” 30-year-old Tarass Filipchak, a Lviv local, told Agence France-Presse. He was building a house at the time when he realized that some of the materials he was using could be repurposed to make the defensive barriers. They have been collected by Ukrainian soldiers and brought all over the country to protect cities and towns. “We went on Wikipedia, looked at where they came from, who had invented them and we started to do the same,” he told AFP. The group of volunteers continues to make the barriers at the end of Filipchak’s driveway. “We couldn’t imagine that we would ever do this. We are peaceful people, humanists,” Filipchak said.

Four men in a workshop as one welds roughly four-feet-long steel beams together to form a cross.

People make anti-tank Czech hedgehogs in Lviv. (Photo by Mykola Tys/SOPA Images/LightRocket via Getty Images)

Eight people stand outside near partially completed Czech hedgehogs, as a welder holds together sections of steel beams.

People making Czech hedgehogs in Lviv, Ukraine. (Photo by Mykola Tys/SOPA Images/LightRocket via Getty Images)

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How are Ukrainian forces taking out so many Russian tanks?

Use this embed to learn about some of the weapons systems the U.S. is sending to the Ukrainian army.