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Shells — and shells: A fortress mentality


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In the 200 years that Castillo de San Marco stood guard on the Atlantic coast of Florida, the fort was never taken. But it wasn’t for lack of trying.


In 1702, the Spanish-controlled stronghold was under siege by British forces from the Carolinas. For almost two months, the fortress safeguarding Spanish trade routes was blasted with bullets and cannonballs.

But mystified Englishmen marvelled at how the walls held fast, seemingly “swallowing” the shells “as though you would stick a knife into cheese.” The frustrated assailants burned the rest of St. Augustine surrounding the fort, but couldn’t breach the walls, which were up to 6 metres or 19 feet thick.

They tried again in 1740, with the same result.

Now we know why. When the teenage daughter of a University of Florida prof wondered about the unusual strength of the walls, she and her dad did an experiment.

In the gift shop at Castillo de San Marco, they bought small samples of coquina (pronounced kuh-KEEN-ah), the material the ramparts are made of.

Then they fired small steel balls at them, at 110-160 mph, to simulate cannon fire, in miniature. A high-speed camera took 200,000 images a second, to record how the samples reacted.

After two years of comparing coquina to other materials, the researchers got the attention of the U.S. Army.

Scientists discovered that, in traditional walls of sandstone, grains lock together in a hard but brittle surface. Projectiles shatter it, sending cracks everywhere and causing the walls to crumble after repeated hits.

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But coquina is a soft limestone made of broken shells from sea creatures. Though the shell fragments are pressed into each other, they aren’t cemented, so they have some give.

When cannonballs smashed into the coquina walls, they crushed the shells hit directly, but surrounding ones just moved out of the way to make room for the missiles.

As Army researcher Phillip Jannotti told Atlas Obscura, “The coquina acts almost as natural foam. The balls sink in, and slowly decelerate.” That understanding may help the military develop new lightweight, blast-resistant materials.

It may also help us develop a better strategy for resisting the many projectiles life fires at us. Though some of us still try to cope with change, stress, and adversity by developing a rigid attitude and hard exterior, that sandstone approach often leaves us brittle and emotionally vulnerable.

We survive the first few onslaughts but repeated hits leave us shattered and exposed.

The alternative is emotional flexibility and resiliency. Though the Bible doesn’t use the word flexibility, it has a lot to say about yielding — the need to surrender preconceived ideas or our own selfish will, or better serve God and others through accepting a change of heart or circumstances.

Our model for that is Jesus who healed on the sabbath; respected women, children and non-Jews; and allowed his followers to break religious traditions like ceremonial handwashing, all of which made Him a target for the rigid and recalcitrant.

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“There’s more at stake here than religion,” He tells critics. “If you had any idea what this scripture meant — ‘I prefer a flexible heart to an inflexible ritual’ — you wouldn’t be nitpicking like this.” (The Message, Matt. 12:6,7)

Of course, there are times when compromise is not acceptable. At one point, Paul says, “Am I seeking the approval of others, or of God? If I were still trying to please people, I wouldn’t be a servant of Christ.” (Gal. 1:10)

But genuine, mature faith involves openness to new ideas and fresh perspectives, being pliant in the transformation of our character, and less vested in the things that don’t really matter. If we’re not, those things probably have too much of a hold on us.

In the face of change, adversity, or even personal attack, we must be like the hummingbird, which goes about its important business by moving in any direction necessary: forward, backward, up, down, sidewise, or hovering in place.

But that can only happen when we lose the pride, self-centredness, or uninformed zealotry that leads to a hard but brittle heart.

Like John the Baptist, we must see Jesus and say, “He must become greater and greater, and I must become less and less.” (John 3:30). But compliance is a slow process

“I have learned how to be content with whatever I have…,” says Paul. “I’ve learned the secret of living in every situation… For I can do everything through Christ, who gives me strength. (Phil. 4:11-13)

Yielding isn’t natural. It has to be learned.

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But the more submission we master, the less damage we’ll suffer from the cannon balls of competition, criticism, and consumerism — to name just a few. The shots life takes at us will still hurt, but they won’t crack or crumble our character and tranquility.

“Don’t worry about anything; pray about everything,” Paul says. “Tell God what you need, and thank Him for all He’s done. Then you’ll experience God’s peace [which] will guard your hearts and minds.” (Phil. 4:6,7).

You can be soft and strong at the same time when it comes to your inner fortress.

Share your thoughts with Rick Gamble at A former TV reporter, he pastors a non-denominational church in Brantford, Followers of Christ (, and teaches media at Laurier Brantford.

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