Six days ago we left the Paris of the 11th Arrondissement, which today again was the Paris of Terror.

In the deadliest day in the city since World War II, seven decades ago, far more than 100 people were killed in six terror attacks, four of which occurred inside the 11th we stayed in for 16 days, ending Saturday. A fifth killing scene was across the street from the 11th.

It is the sort of thing that makes a person think about where they have been, and what they saw, and semi-close calls.

And, especially, why the 11th might have been singled out by the murderers.

The apartment in which we stayed is on the same street as one of the attacks. It is about 250 yards away; we walked past the future crime scene 15 or 20 times.

Three other sites where violence played out were south of our base, closer to the Bastille than to the Place de la Republique.

We had twice walked past the cite of the greatest number of killings, the Bataclan concert hall, without noticing it. It was a few yards to our right while we, ironically, were making a pilgrimage to the Charlie Hebdo terror scene — also in the 11th (hence, the “again” up in the first paragraph) and very near the Bataclan. A three-minute walk.

Two more sites, we probably passed without knowing it. On a bus. In a cab. Anyway, we had close proximity with five of the six scenes of violence, the exception being the Stade de France, which is outside of Paris proper.

Why would all the attacks happen in the 11th?

I do not belong to any law enforcement organization. I do not have access to inside information. But I have some ideas.

–I had been to Paris 15 or 20 times and not spent more than an hour or two in the main (northern) part of the 11th. The 11th is not a tourist destination and, from our recent time there, I do not recall seeing a police officer — not one. (Unless you count guys rolling by in the backs of vans headed somewhere else.) A person does see security near the famous monuments … where the really big crowds gather and where the tourists go … but that is not the 11th. Thus, attacks in the 11th are unlikely to meet up with some initial police presence. I suppose that makes the 11th one big “soft” target.

–The 11th is the most densely populated arrondissement. It has dozens and dozens of places where quick and violent attacks could yield several casualties, which urban terrorists tend to like. Crowds on the street, for starters, but there are lots of nodes of activity, too. Bistros, cafes, bars, many of them crowded with the young people who seem to constitute a majority in the 11th. And this was on a Friday night, a particularly intense time for socializing, as we had seen on the previous three Friday nights in the 11th.

–Also, we can assume police in Paris are thinking “the attackers probably lived in the 11th”. The site of your attack is probably a place with which you are familiar, yes? Where a murderous resident might already have ideas on targets of opportunity — such as the concert hall that can hardly be seen until you are in front of it or the restaurant your associates never go to. Also, the 11th is a thoroughly multicultural arrondissement, and the attackers could live there without standing out.

It will take days to know more about what happened and identify the attackers.

Meantime, we can speculate at why the neighborhood where we just lived for half a month was targeted. We can feel a sort of second-hand affinity for the people there. We can picture where some of these scenes of horror played out.

And we can understand just how random are these intersections with violence.

Attacks of Paris seem particularly vile, and President Obama perhaps summed it up in a statement tonight.

“Once again, we’ve seen an outrageous attempt to terrorize innocent civilians,” he said.

“This is an attack not just on Paris, it’s an attack not just on the people of France, but this is an attack on all of humanity and the universal values that we share.”

He added: “Paris itself represents the timeless values of human progress. Those who think that they can terrorize the people of France or the values that they stand for are wrong.”