Billionaire tech mogul Elon Musk has reignited debate over population growth, warning that declining birth rates could lead to societal collapse.

In a series of tweets, Musk urged parents to have at least three children, citing historical examples like ancient Rome to stress the dangers of population decline.

“People who have kids do need to have 3 kids to make up for those who have 0 or 1 kid or population will collapse,” he tweeted.

“Low birth rate was the primary factor in the fall of Rome and all civilizations that enjoyed an extended period of prosperity with no serious external threats. Shockingly overlooked by most historians,” Musk added.

The Tesla and SpaceX boss has always been vocal about population concerns, previously warning that a “population collapse” could be a bigger risk to civilization than climate change.