Suleiman the Magnificent earned his epithet, at least militarily. The Sultan of the Ottoman Empire for 46 years, he spent much of his time on campaign. Hungary and Persia felt the brunt of his martial genius, but perhaps his most famous victory was the Siege of Rhodes in 1522. It was a grudge match.

The island of Rhodes was a blemish on the Ottoman Empire's record. It was held by the Order of St. John (also known as the Knights Hospitaller), and it withstood the Ottoman troops' siege in 1480. The Order of St. John had first been established to care for sick pilgrims in the Holy Land, but had been beaten back and militarized as Christians lost control over the region. At Rhodes they stood firm, but both sides knew that more conflict was inevitable.

As soon as the enemy boats had disappeared over the horizon in 1480, the Order began raising and thickening the walls around their stronghold. By 1522, their fortifications stood against the barrage laid down by the naval blockade of Suleiman's military. This did not discourage the Sultan. He knew there was another way in: underground.

Engineers had long been an integral part of warfare. They helped cities create better defenses, with high, strong walls punctuated by slits for firing arrows—or crenelations for releasing boiling oil. For their part, army engineers crafted siege engines to hurl things against or over walls. Tunneling under walls and blowing them up from beneath was also a well-established siege technique, dating back to several centuries BC.

The Siege of Rhodes, however, was one of the best-documented cases of a war won and lost by engineers, not because of the Sultan's offense, but because of Rhodes' defense. To maintain the integrity of their walls, the defenders of Rhodes brought an early genius of military engineering, Gabriele Tadini.

Tunnel warfare and surveillance

Military mining was equally hard on the body and the mind. Tunnelers worked in darkness, digging corridors that could collapse on them and knowing that, somewhere in the earth, the enemy was doing the same. If one group of miners detected another, they could dig toward the enemy tunnel and blow it up.

Tadini, who had trained first as a doctor and then as an engineer in the Venetian army, came to Rhodes specifically to fight the Ottoman empire. The first thing he did was eliminate the haphazard nature of military tunneling. He put the citizenry to work creating a well-planned underground network in and around the walls, making a kind of grid of established tunnels.

He peopled these tunnels with specially-trained monitors, generally children or people too old to fight. Each of the monitors kept their ears close to what must have looked to them like a tambourine. This invention of Tadini's was made from a parchment membrane stretched across a drum-like frame. Tiny bells hung from the edges of the drum. The slightest vibration would set the bells jingling and allow the monitors to detect and slowly close in on an Ottoman tunnel in progress.

After a tunnel was detected, Tadini supervised a careful digging effort toward that tunnel. This was a nerve-shredding process—moving toward an opposing force, never knowing when the opposition would blow their charge. Even if the other side was nowhere near ready to lay a mine, a tunneler faced other dangers. Getting too far from the surface meant suffocation. One of the reasons Tadini was prized as a tactician was his ability to keep the tunnels well-ventilated.

Once the miners got close enough to the opposing tunnel, it was time to blow the other tunnel to smithereens. This created its own problem. Too big a blast, and the defenders would fell their own walls. Here, another Tadini innovation kept Rhodes intact. Most tunnels and vents were straight, which saved effort on the part of the miners. But that meant, once a mine was detonated, the blast came roaring outwards. Tadini directed the construction of spiraling vents, which dampened the force of each explosion and limited the damage to the earth around Rhodes.

And so Rhodes stood, behind its walls, on top of an innovative network of monitoring tunnels, vibrating with the workings of a corps of engineers seeking out and destroying the mines of the invaders.

The end of Tadini

Unfortunately for the Order of St. John, Tadini's tunnels were not a permanent solution. Even the most advanced monitoring network eventually misses a signal. As the months went on and the besieged force lost supplies and people, their only hope was for Suleiman to lift the siege. This, he did not do.

Suleiman also had a bit of luck when Tadini, who regularly scaled the walls to calculate the best way to bombard the enemy, was shot in the eye and gravely wounded. Eventually, the Sultan's forces managed to tumble the walls in two sections of the city, which lead to hand-to-hand fighting devastating to both sides.

Still, the defenders hung in there until Tadini confirmed to Philippe Villiers, the Grand Master of the Order, that the city was no longer defensible. Villiers had ignored the many warriors who told him the same, but listened to the engineer.

Suleiman was respectful and generous in victory. The citizens of Rhodes were to be exempt from both taxation and conscription for the next five years. Tadini was allowed to leave. He went to the colonies of Genoa, where he again fought invading Ottoman forces and again lost.

The Order of St. John was allowed to leave in peace and build a new fortress elsewhere. They did so on Malta, where their walls could be built on stone and therefore could not be undermined. Toward the end of his life, Suleiman sent a force to conquer Malta. This time the siege failed, in part because he was not there to keep order or impose his implacable will.

Despite Tadini's losses, his methods have continued to influence combat into the present. Mining and countermining, with all their attendant surveillance and engineering, are still staples of warfare.