On a recent trip to Paris, we arranged to meet up with a friend, a Canadian architecture-school librarian. As the three of us wandered about Montmartre, she asked us an intriguing question: “What are those spiked things for?” I replied, “They mean don’t go there.” They are more than mere barriers – they are designed to intimidate.

Some are simple, with only a single layer or row of spikes. Others, such as this fierce specimen, threaten intruders with evisceration.

All of them – and I include only a few of the many I have photographed – have one purpose: to tell you not to even think about going there and to stop you very painfully if you try. The two shown above are warnings not to climb up the drainpipe to gain entry to anything you might otherwise plan on breaking into.

Sometimes they are less obvious. On a lazy August day, we watched boys playing soccer on the wide, shady sidewalk in front of an attractive Ministere des Finances building. It was an idyllic scene.

But take a closer look. Cast your eye upwards along the grey front to the right of the group of boys. Here, let me help you with a telephoto shot.

The rings of metal thorns – even when reflected in a windowpane – are all about business, the business of saying: don’t go there.

On another building, the U-shaped light well that brightened the interior of the apartments might have provided an ideal entry point for those with evil intentions. The message of the intimidating barriers is clear: Think twice about it.

On the building below, the downspout ring of iron thorns seems lacking in enthusiasm but the bottom two levels of windows are barred. Moreover, there are three security cameras.

Now take a closer look at the barriers at the side of the building. It would be very dangerous to stand on the pillar or to try to get past it.

Even those who might gain access to the higher levels will find that many buildings have barriers to moving sideways from one building to another. Some manage to be ornamental as well as intimidating.

Others are less subtle. The closer you get the louder they seem to scream their message.

As we paused to look closer, we noticed the netting that usually indicates there is structural work to be done on whatever is underneath. Another good reason not to climb.

And the nearer you get to your imagined destination the more you know you ought to be somewhere else.

And it is not just people who get the messages. In the inner courtyard of Le Petit Palais, where we paused for lunch, we noticed a few messages directed at the pigeons: don’t even try to land or perch here. Your feet will regret it.

Best to just fly on by. There are better career opportunities elsewhere. How about acting as a “fascinator” at a regal gathering?

Text and photographs by Norman Ball.