Typically, the security at a modern World Cup has many layers. They block off streets to traffic in a kilometers-wide perimeter around the stadium on game day. Nobody without a ticket is allowed to get anywhere near the gates. Everyone who goes inside is put through a body search or a metal detector.
That system collapsed utterly here on Tuesday afternoon before the Spain-Chile contest. This is proof that Brazil was not ready to host this tournament. That failure will reverberate from now until the opening of the Rio Olympics in two years time.
In a shocking lapse, about a hundred panicked Chilean fans were allowed to run through the cordon outside Rio's Maracana stadium and into the main press centre.
At first, they came in a great wave. Journalists just outside the doors – standing in what's become the de facto smoking section – seemed amused. As they bottlenecked at the entrance, doors buckled and glass shattered.
It was about an hour before kickoff. Inside, as many as a thousand international press were sitting at long tables, tapping away.
When the invaders reached the middle of the room, they paused, presumably looking for a door that led toward the pitch. They slowed to a walk. Journalists began to get out of their seats. Many began filming.
With cocksure ease, a few ambled over to temporary walls at the far side of the entrance and began tearing at them. The walls collapsed easily, and then in a chain reaction. Several began tumbling heavily onto desks, bringing lockers and large flat-screen TVs with them, in a pant-wetting bang. Amazingly, no one was seriously hurt.
Some journalists were now scrambling away from the scene, while dozens more poured in to film and take pictures. This will have been the best-documented construction failure in human history.
There are hundreds of heavily armed riot police out in the streets outside the Maracana, but very few inside the perimeter. That domain was entirely left to private security. As a direct result of Tuesday's fracas, that order has now been reversed – police will patrol stadiums from here on in.
On Tuesday, a handful of stewards were left to combat the invaders, desperately trying to push them back into a service corridor that runs behind the room. The Chileans were shouted off. About 90 were quickly arrested. A few managed to sneak off.
In a hastily prepared statement, FIFA and the local organizing committee condemned the act, but had nothing to say about how it happened, or how it might be prevented in future.
Brazil has now been humiliatingly been put on notice that their preparations for this event are woefully sub-standard. Everyone working the tournament already knew that. Aside from what's happening on the pitch in front of the TV cameras, nothing works particularly well. This security boondoggle allowed an embarrassing look behind the curtain.
For all the stick Sochi took for its preparations, the idea that this sort of thing might have happened there was unimaginable. The Russians understood that the one system that could not be allowed to fail was security.
What makes this particularly worrying is that it happened at the Maracana, and not just once. Nine Argentinian fans were arrested after sneaking through security at Sunday's game.
Unlike many of the newly built stadiums around Brazil, the Maracana has a long history of hosting huge, often unruly, crowds. One came here presuming that, in this building at least, things would go smoothly.
They haven't, for a variety of reasons.
First, fans are allowed far too close to the arena before they must present their tickets. Hundreds are sitting a few feet from the doors holding up signs looking for ducats.
Drink is a problem as well. Years ago, in an effort to combat out-of-control hooligan violence, Brazil outlawed the sale of alcohol at football matches. FIFA insisted that ban be temporarily over-turned, in order to suit its brewery sponsors. Locals refer to that change as the "Budweiser Bill." A fair number of the supporters here are blind drunk by kickoff.
Most alarmingly, there is an incredibly wrong-headed focus from security. Bags are assiduously checked for contraband – water and food. FIFA wants to wring every possible concession dollar out of this venue.
But they're not paying a whole lot of attention to the people themselves. While we waited in line on Tuesday afternoon to go through a metal detector, four fans in Chile jerseys simply moved a barricade aside and walked through an unmanned metal detector. Only a passing volunteer had the sense to notice them. They were quickly hustled out, looking confused.
Two hours later, it happened again, and more spectacularly.
One wonders now what a country like the United States or Iran thinks of their safety. This came less than 24 hours after a suicide bomber attacked a World Cup viewing party in Nigeria, killing 14 people.
Might the ease with which fans were able to penetrate a high-security area embolden someone far more dangerous? That question will subtly haunt the remainder of this tournament, and it will not go away until the Olympics have come off safely. It's an awfully long time to worry.