In 1400 BCE, Joshua and his troops marched around the walls of Jericho along with seven priests, blowing rams’ horns once a day for six days. On the seventh day, they marched around the walls seven times. This time, the blasts of the horns were followed by a shout from the entire army — and “the walls came tumbling down.” With no further resistance, the city was destroyed.

The Great Wall of China was begun in the 7th century BCE, and eventually stretched 13,000 miles when it was completed more than 2,000 years later. It often proved ineffective, and was considered more of a “scarecrow” than a defense. The Chinese army in front of or behind the wall ready to slaughter the enemy provided the real protection. In addition to other failures, the Great Wall was breached several times by Genghis Khan, whose army was equipped with crude weapons by today’s standard.

And who paid for the Great Wall of China? Chinese taxpayers. One commentator noted that the wall was so expensive that during the Qin dynasty (221-227 BCE) “it crushed their economy, sparking a rebellion.” And according to a popular legend, the Han dynasty (206 BCE – 220 CE) financed some of the staggering cost with a state-sponsored lottery.

The wall surrounding Vatican City was built in the 9th century by Pope Leo IV. Despite the 39-foot fortification, several popes fled for fear that approaching enemies would easily breach the wall. In 1494 Pope Alexander VI escaped through a secret half-mile long passageway when Charles VIII of France invaded Italy, for example.

So, contrary to President Donald Trump’s claims, walls aren’t always effective. Nor, as he declared, is the Vatican encased in the mother of all walls. In fact, today there is no complete wall around Vatican City. Visitors can stroll down the Via della Conciliazione, which opens onto St. Peter’s Square.

And what characteristics are shared by walls that actually worked? Three factors: relatively short lengths, multiple layers of obstruction, and the most essential factor — the use of lethal force against violators.

Only 27 miles of the 96-mile Berlin wall divided East and West Berlin. The initial wall was later fortified by “incorporating a row of subsidiary walls, trenches, electric fences, and an open ‘death strip’ overseen by armed guards in 302 watchtowers.” The wall was also protected by one million land mines and 3,000 attack dogs. Guards were ordered to shoot anyone attempting to escape.

The Israeli Gaza wall is a combination of a barbed-wire fence and a 10-foot metal fence with electronic sensors that instantly report movement along the fence. It has significantly reduced the number of murderous terrorist attacks. Nevertheless, after the discovery of dozens of tunnels under the present fence, Israel is now building a concrete wall spanning the entire 40-mile border with the Gaza Strip. It will extend deep into the ground, and powerful sensors will detect tunnels that approach the wall. When all else fails, the Israeli military is prepared to respond with lethal force.

Will Donald Trump authorize lethal force when his wall fails to stop migrants seeking asylum? He has already given his frightening answer: “If they have to, they’re gonna use lethal force. … I’ve given the OK.”

If earlier walls were breached by crude weapons, it’s not likely that Donald Trump’s medieval-style wall will stand up against 21st-century technology. To effectively police a 1,900 mile wall is virtually impossible. That’s why ladders and tunnels will still let migrants outflank Trump’s wall. And how will his wall stop helicopters and passenger drones? A Chinese model of a passenger drone will be available by mid-2019.

Let’s hope Congress stands firm and that Trump’s plan for a medieval wall comes tumbling down.