Tower Power

People continued to scramble up the rising human tower, adding more and more levels. Finally, a few small children scaled all the way to the top. One stood proudly at the highest point and raised her hand in salute. Spectators crowded in the square erupted into cheers. The children then shimmied down the tower, followed by a cascade of fellow climbers from the highest to lowest level, until the structure was completely dismantled. “It was like a waterfall of people,” says Hamalainen.

What Hamalainen had witnessed was the Spanish tradition of building castells—the Catalan word for “castles.” Teams of castellers, or “castle makers,” in Spain’s northeastern Catalonia region have been constructing these human towers since the 1700s (see Catalan Culture). Back then, a five-level tower was an impressive feat. But today, the most highly skilled teams can reach 10 levels.

People kept climbing the rising human tower. They added more and more levels. Finally, a few small children scaled all the way to the top. One stood proudly at the highest point and raised her hand in salute. The crowd in the street cheered. Then the children slid down the tower. Their fellow climbers followed, from the highest to lowest level. Quickly, the structure came completely down. “It was like a waterfall of people,” says Hamalainen.

Hamalainen had just seen the Spanish tradition of building castells. That’s the Catalan word for “castles.” Teams of castellers, or “castle makers,” form these human towers. They’ve been doing this in Spain’s northeastern Catalonia region since the 1700s. Back then, a five-level tower was a huge feat. But today, the most highly skilled teams can reach 10 levels.

Castells can take many shapes, but they all have three basic parts (see Engineering a Castell). The base, or bottom level, contains the most people, sometimes hundreds. The trunk consists of several levels and rises from the center of the base. The crown sits on top. It’s usually formed by kids who are light enough for those below to easily support.

Large human towers may appear to put an overwhelmingly heavy burden on the castellers on the lowest level. But Josep Soler, a mechanical engineer and former casteller in Catalonia, says the combined load pushing down on them isn’t as crushing as it looks. “The people at the base work together as a team so that forces are divided among them,” he says. To share the load, the castellers at the center of the base intertwine their arms into carefully planned positions. Hundreds of teammates then surround them, arranging their bodies into an organized pattern that provides support inward and upward. All that pushing toward the center helps counteract the downward force of the weight of the trunk and crown.

Castells can take many shapes, but all have three basic parts. The base is the bottom level. It contains the most people, sometimes hundreds. The trunk has several levels. It rises from the center of the base. The crown sits on top. Kids usually form the crown, because they’re light. It’s easier for those below to hold them up.

Large human towers are very heavy. They may appear to put an impossible burden on the castellers at the bottom. But the combined load pushing down on them isn’t as crushing as it looks, says Josep Soler. He’s a mechanical engineer and former casteller in Catalonia. “The people at the base work together as a team so that forces are divided among them,” he says. The castellers at the center of the base thread their arms into certain positions. That helps them share the load. Then hundreds of teammates surround them. They place their bodies in a pattern that pushes inward and upward. As they push toward the center, this helps offset the downward force of the tower’s weight above them.

Supporting a tower’s immense weight is just one challenge castellers face. They also need to make sure a tower remains stable as it rises higher and higher. “The difficulty is not only how much load I will sustain on my body but also that this load will be moving during the construction of the tower,” says Rosset.

Castellers strive to keep the tower’s center of mass—the point around which an object’s mass is evenly distributed—balanced directly over the levels below them. As team members ascend the tower, they don’t want to make it shift or sway. Climbers try to align their weight close to the middle of each body they’re climbing over. That way the castell’s center of mass doesn’t tilt too far to one side. Too much tilt could cause the whole tower to collapse.

Castellers must support a tower’s great weight. But that’s just one challenge they face. They also need to keep the tower stable as it rises higher and higher. “The difficulty is not only how much load I will sustain on my body but also that this load will be moving during the construction of the tower,” says Rosset.

The tower’s center of mass is the point around which its mass is evenly spread. Castellers work to keep this point balanced over the lower levels. So team members climb the tower carefully. They don’t want to make it shift or tilt. Climbers try to keep their weight close to the middle of each body they’re climbing over. That way, the castell’s center of mass doesn’t tilt too far to one side. Too much tilt, and the whole tower could fall.

Falling is a risk for castellers and another reason a tower’s base contains so many people—up to 600 castellers for the tallest towers. “They act as a human mattress,” says Rosset. When a castell tumbles—which happens in about 3 percent of attempts—the people in the lower levels absorb the impact of their falling teammates, preventing them from hitting the ground with full force. The youngest—and highest-climbing—members of a castell team also wear helmets for extra safety.

Falling is a risk for castellers. It’s also another reason to have so many people in the base. The bases of the tallest towers contain up to 600 castellers. “They act as a human mattress,” says Rosset. A castell falls in about 3 percent of tries. When that happens, the people in the lower levels absorb the fall of their teammates. This saves the climbers from hitting the ground with full force. The youngest members of a castell team are also the highest climbers. They wear helmets for extra safety.