Not many cities come with two-thirds of a moat.

The big map on the front page last Wednesday under the headline "Shutdown, Pa. 15222,'' nicely showed how the Allegheny and Monongahela rivers make it easy to deny access Downtown from two sides. Close a few bridges and you're done.

Our natural moat may have had zilch to do with Pittsburgh hosting the G-20 summit, but it figures in the calculations that law enforcement strategists make. The trick is how to keep everyone safe without trampling on anyone's constitutional right to free assembly.

This many guys with guns haven't stared at maps of the Point in at least 250 years, so I decided to head down to the Senator John Heinz History Center to see how the current plan compares with the strategies of the French and Indian War.

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PG STORE

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Brian O'Neill's book, "The Paris of Appalachia: Pittsburgh in the Twenty-first Century," is available in the PG store.

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Andy Masich is president and CEO of the History Center. He's also the go-to guy for a quick lesson on the world war that was touched off hereabouts by a young George Washington. I found him Friday at the "Clash of Empires'' exhibit, hovering over a scale model of Fort Duquesne.

Mr. Masich (rhymes with "basic") made it clear from the outset that he isn't worried about any imminent siege of Pittsburgh. The museum is open all next week for any visitor who wants to learn how we evolved into whatever it is we are.

Right now, a lot of what we are is overreacting.

"There hasn't been this much wringing of hands, gnashing of teeth and pulling of hair since the Pinkerton barge landed in 1892,'' Mr. Masich said.

He was referring, of course, to the Homestead Strike, which began when Henry Clay Frick locked out the workers at Carnegie Steel. That led to an armed fight between workers and Pinkerton agents on July 6, 1892. Four thousand state militia took control of the town within the week.

(Anarchists were in the news then, too. A Russian-born man from New York, Alexander Berkman, was so angry with Frick, he came here and shot Frick three times and stabbed him twice. Whatever else he was, Frick was one tough dude, and survived. Berkman spent the next 14 years in Western Penitentiary. In an act of prosecutorial nostalgia, police may use the old prison again this week for booking anarchists.)

Back to the French and Indian War.

The first time Washington laid eyes on the Point he knew that whoever controlled it, controlled the West, but the French beat the British and colonials to it. Fort Duquesne was well-designed, yet the French ultimately destroyed the fort and fled in November 1758 because "they did the math,'' Masich said. Not enough food + Not enough ammo = We gotta get out of this place.

Wanting more current info, I called retired Maj. Gen. Robert H. Scales, former commandant of the U.S. Army War College in Carlisle and now a defense consultant.

Gen. Scales said the question of the tactical advantages and disadvantages of "defending'' the Point is an interesting one, but it is irrelevant apart from the obvious point of the rivers enclosing whatever might happen Downtown.

The overwhelming majority of protesters will be peaceful, he said, but any flareups will have more to do with the psychology of mobs than the terrain. Trouble generally doesn't come so much from planned activity or leadership but from spontaneous acts that "just sort of bubble up.''

"As a general rule the unpleasantness is generated by a small percentage,'' he said. Such events "are more akin to chaos theory than organizational theory.''

I'd add that chaos can begin on either side when police and protesters meet.

I'll end by trying to broaden our understanding of "anarchist,'' which we've heard more times in the past month than we had in the previous decade. My financial adviser, Joe Hadobas, has this twist:

"We have a term for anarchists on Wall Street: investment bankers. Both are defined in this manner: Willful destroyers of other people's property; people acting without regard to their actions; people who serve no obvious social utility; people whose sole focus is self-interest masquerading as serving a greater good; people who scoff at rules and regulations.''

It's a toss-up who's capable of more damage, the folks in suits or the ones in black T-shirts, but both should be well represented this week.