The death toll in 1990 was over 1,400. It was 270 in 1994, 118 in 1998 and 251 in 2004. Hundreds of people crushed, trampled and choked to death. Anders Johansson knew Mecca the way every prospective panic researcher gets to know the city: in terms of casualty numbers.
It is Jan. 12, 2006 and Johansson is experiencing the reality behind the statistics at first hand. He has travelled to Mecca on the invitation of the Saudi Arabian Ministry of Municipal and Rural Affairs. Johansson is here to study the flow of pilgrims -- the subject of his dissertation at Dresden University of Technology.
As the sun reaches its zenith, Johansson watches a sea of colored dots on a monitor. The dots are pilgrims dressed in white robes, on their way to the three pillars in a valley outside Mina, several kilometers from Mecca. The pillars symbolize the devil, who will now be ceremonially stoned. It is here that Abraham is said to have once chased the devil away by throwing stones. These days, the area is under video surveillance.
Around 11:53 a.m., the pilgrims at one of the entrances to the area begin pushing each other about. The crowd forces its way forward. At 12:19 a.m., the flow of pilgrims is stalled, and at 12:30 a.m. a gap forms suddenly in the midst of the crowd. Some of the pilgrims have fallen to the ground and others are stumbling over them.
Anders Johansson senses what is happening at this moment and has to sit down. He knows that when so many people crowd together, the body is exposed to pressure equivalent to more than one ton -- the weight of a small car. Tragically, the 2006 stoning entered the annual statistics with a total of 364 deaths.
When Anders Johansson returns to his office at the Dresden University of Technology a few days later, he is carrying video tapes in his luggage: films of people pressed closely together and forcing their way forward. Now he must examine the cause of the catastrophe. He does not have much time. The next pilgrimage will begin on Dec. 28, 2006.
After the mass panic on Jan. 12, authorities had had enough. They resolved to regain control of the growing streams of pilgrims and sought advice from Dirk Helbing of the Dresden University of Technology.
Helbing, a youthful six-footer, is a pioneer in the field of panic studies. His scholarly articles on the flow of pedestrians and cases of stampedes in football stadiums are the most frequently quoted within the field.
Helbing put together a team of German experts for the Saudis, comprised of traffic planners from Aachen, logistics experts from Dresden and his doctoral student Anders Johansson. For Helbing, Mecca is "the biggest pedestrian problem in the world."
Every Muslim is required to make the pilgrimage to Mecca once in his life in order to prove his obedience to God. The pilgrimage, known as the hajj, takes place every year on five days during the last month of the Islamic lunar calendar. The Prophet Muhammad originated the hajj tradition in the seventh century. First, hundreds of Muslims came -- then thousands, then tens of thousands. By January 2006 the number had climbed to 3 million.
That makes Mecca, the place of redemption, a place of risk. Nowhere else in the world do as many people crowd onto as small an area. The valley at Mina is about three kilometers by three kilometers (1.9 miles by 1.9 miles) large. Every year, it's as if Berlin's entire population were to converge on the city's Schönefeld airport.
The pilgrims arrive from more than 100 different countries. For most, it is the first time they have flown in an airplane. They land at Jeddah airport by the Red Sea, which opens a special terminal during the hajj. Hundreds of thousands of them are illiterate, and they speak dozens of different languages. In some of their countries of origins, the custom is to walk on the right side of the street; in others, the custom is to walk on the left. The situation involves "many uncontrollable variables," Dirk Helbing notes soberly.
Researchers have learned from computer simulations that people who want to escape from a room may block each others' way in a phenomenon known as "escape panic." When those at the back push and the exit at the front is blocked, people are crushed to death. But the case in Mecca presented the scientists with a puzzle: People have died even in open areas there.
In order to evaluate the 2006 videos, Anders Johansson developed a computer program to count the pilgrims. When people crowd into a subway or an elevator, three or four of them can fit onto one square meter (10.8 square feet). In scenarios developed by researchers studying pedestrian behavior, based on the size of the average European, the maximum density was six people per square meter. In Mecca, the number per square meter was 10.
Helbing and Johansson scanned the video material for early warning signals announcing the start of a mass panic. When they viewed the film at 10 times the normal speed, they found what they were looking for: Twenty minutes before the catastrophe, the first patterns of irregular movement appeared in the crowd, which had previously been flowing at an even pace. Shortly before the catastrophe, blocks of hundreds of people suddenly began jerkily drifting in every direction. What had appeared fluid just a moment before was now behaving "like the earth during an earthquake," Helbing explains. Crevices appear between blocks of people. Some people lose traction. Those people who fall down may never stand up again.
'It Was Pure Chaos'
The catastrophe typically occurs on the last day of the hajj. By then, the pilgrims have already spent two days in the tent camps of Mina. From there they walk a few hundred meters to the three pillars every day in order to throw a total of 49 pebbles at them, in accordance with a fixed pattern. On the fifth day, after their midday prayers, they are expected to throw their last 21 stones -- seven at each pillar. Most of them then want to begin their homeward journey. This causes the throng to increase dangerously just as the sun is at its zenith.
In order to deal with the onrush of pilgrims, the authorities had a bridge built during the mid-1960s. Three holes were left for the pillars on the middle lane, surrounded by a balustrade. That allowed pilgrims to toss their pebbles both from the ground and from the bridge. But the number of accidents has been rising since the 1990s. The ramp leading onto the bridge now seems as small as the proverbial eye of a needle.
Following the 2006 catastrophe, authorities had the old bridge torn down. They have plans for a new and even larger one. In the future, the stoning ritual will take place on four different levels as well as on the ground. The planned construction will be larger than Berlin's central train station, with emergency exit tunnels, helicopter landing pads and a conveyor belt by which to remove the falling pebbles. Two years earlier, the pillars had already -- with the approval of religious scholars -- been enclosed in elliptical concrete walls, in order to increase the area available for stoning. Once completed, the bridge will hold as many as 5 million pilgrims.
The first level of the new bridge was scheduled for completion in time for the 2006 hajj, with a new level to be added every following year. Cancelling the pilgrimage because of construction work would be unthinkable. In December 2006, the new security measure simply had to work.
The project of making Mecca safe necessarily involved a clash of cultures. Germans and Arabs, imams and generals, civil servants, physicists and engineers were all involved. "A lot of persuasion was needed," says an employee of the Saudi Arabian Ministry of Municipal and Rural Affairs who coordinated the measures. But the goal was the same for all the parties concerned: Getting people from A to B and back again, safely.
Mecca's One-Way System
The most controversial proposals included introducing one-way traffic. That idea was the brainchild of Dirk Serwill and Reiner Vollmer, two traffic planners who developed, along with the Aachen-based engineering company IVV, the mobility guidelines for the Catholic World Youth Day held in Cologne in 2005. A field west of Cologne, 50 kilometers (31 miles) of provisional roads, more than a million pilgrims and 12,000 portable toilets were what they had to work with. When it was over, Serwill said to himself: "There will never be anything like this again."
He was wrong. This time, the Saudis didn't just want to build a bridge. They also wanted to find a better way of directing the flows of pedestrians that make their way from the tent camps to the bridge. The engineers from Aachen were given the task of finding a solution to the problem. But they were unable to travel to Mecca themselves in order to examine the situation on the ground -- only Muslims are allowed to visit the holy city. And so the Saudis sent them photographs of the stoning ritual. The images showed pilgrims streaming diagonally across the square. Some had set up their own tents. Merchants and barbers sat on carpets in the midst of the turmoil. "It made us swallow hard," says Serwill. "It was pure chaos."
Several flows of pilgrims came together at the ramp leading onto the old bridge. Serwill's metaphor is that of a washing machine: Seen from above, the flows of pilgrims blended together in a circular spinning motion. "It was inevitable that someone would stumble sooner or later," he says.
He showed the Saudis a photograph taken at the World Youth Day. The image shows a fence in the middle of a road. On one side of the fence, a stream of young people walks towards the pope. On the other side, there is room for ambulances. Many such one-way streets were set up at the time.
But that was in Germany, not in Mecca. Saudi Arabia's military officials were skeptical. Then again, had the World Youth Day not gone off smoothly, apart from a few overcrowded train stations? And had a section of the autobahn not been closed off on the suggestion of the engineers, turning 13 kilometers (8 miles) of the closest thing Germany has to sacred ground into a parking lot for buses? Maybe that was what convinced the Saudis. They decided to give Serwill and Vollmer's one-way street proposal the go-ahead.
The traffic planners sketched red and green streets onto a map of Mina: green for the people on their way to the stoning ritual, red for those coming back. They marked certain areas that were to be closed off and opened up only in case of emergencies, like the plains along the River Rhine that can be flooded during high water. And they marked positions for fences to be set up in in order to channel the pedestrian flows. "Better to have congestion on a 10-meter-wide street than on a 50-meter-wide square," says Serwill. The Germans made sure everything was organized. Rainer Vollmer sums it up in one word: "structure."
A Matter of Life and Death
The new structure that the Germans introduced includes what is probably the biggest time schedule in the world, developed by logistics expert Knut Haase of Dresden University of Technology. Haase allotted a route and a time for the stoning ritual to 30,000 groups consisting of 100 pilgrims each. Traffic psychologist Bernhard Schlag advised the Saudis on the ideal design of the traffic signs, and the Hajj Ministry made an educational film on the re-organization of the stoning ritual. It was shown to the pilgrims on the plane to Mecca.
Still one problem could not be solved by any scientist or regulated by any engineer: the question of life and death. For many pilgrims, dying during the hajj is not the worst of fates. After all, such a death guarantees an immediate ascension to heaven, they believe. So why observe security regulations?
The authorities invited religious scholars to workshops and politely asked them to distance themselves from such interpretations of Islam. It was all they could do.
The hajj of the year 1427 (by the Muslim calendar) began on Dec. 28, 2006. When the pilgrims arrived in Mina on the third day, they were faced with a construction site. There were cranes and raw concrete everywhere. Iron bars rose from the bridge's support columns. Construction workers had set up the floodlights at the last moment. The first level of the bridge had just been completed.
Anders Johansson, a Muslim himself, had travelled back to Mecca. His computer program was counting the pilgrims on his monitors.
The Germans were met with a few small surprises in the city of pilgrims: An unusually large number of people had arrived that year. The second day of the hajj happened to be a Friday, which increases the date's religious significance. Moreover, some buses dropped the pilgrims off at the wrong location, some VIPs drove diagonally through the flows of pilgrims in their cars and many pilgrims from Iran avoided the bridge because they wanted to stand on solid ground during the stoning ritual.
But the vast majority of the pilgrims obeyed the rules. They followed the green arrows directing them to the columns. The pilgrims threw their pebbles and murmured their prayers, then walked back to their tents via different roads. Some emergency areas had to be opened up, but that was it: There were no accidents, no outbreaks of panic and no casualties.
So is Mecca safe now? "It's safer," says panic expert Helbing. "We will probably never achieve 100 percent safety." That would involve moving mountains.
But one year without casualties makes a great difference. As a gesture of thanks for the one-way streets, Dirk Serwill was given an enamel sign from the bridge, complete with an inscription expressing the authorities' gratitude. He will continue his work as a planner when the new bridge levels are built. Anders Johansson wants to improve his computer program so it will automatically warn of imminent outbreaks of mass panic.
And Dirk Helbing's thoughts have taken a meditative turn. "Nothing happens by chance with me," he says. "But this project somehow felt like destiny. Maybe Allah wanted us to help."
The German version of this article originally appeared in the 6/2007 edition of the magazine Zeit Wissen.