Who says a border wall would be useless?

Walls apparently make excellent mounts for drug-launching machines.

Drug smugglers recently repurposed a section of border fence east of the Douglas port of entry, using it as a foundation for a makeshift catapult.

On Friday, U.S. Border Patrol agents noticed a group of people fleeing a spot on the south side of the border.

When they pulled up, they saw a "catapult system attached to the south side of the border fence," according to the Border Patrol.

A search of the area turned up bundles of marijuana weighing a total of 47 pounds that were believed to have been launched by the catapult.

The agents contacted Mexican authorities, who seized the machine as evidence after the Border Patrol cut it down from the fence.

A U.S. Border Patrol spokesman said that "like a good neighbor," agents let the machine drop to the south side after dismantling it.

The Mexican authorities are no doubt conducting a thorough investigation — right?

The spokesman didn't have any statistics available immediately on the number of catapults that border agents have found in recent years.

Several catapults and weed-shooting cannons have been found since one of the contraptions made headlines in 2011.

No one knows if the border wall that President Trump ordered to be built would slow down the trend, or spark an arms race for bigger and more-powerful catapults.

But Friday's discovery shows that drug smugglers could incorporate the new wall into plans for a new generation of weed-shooting cannons.

Eventually, the cartels could rediscover the reason that ancient people invented catapults — to take down walls.