New York Mayor Bill de Blasio said on MSNBC Monday morning his city will ban “inefficient” steel and glass skyscrapers and begin mandating the use of wattle and daub, a type of building material first used more than 6,000 years ago.

“The biggest source of CO2 emissions in New York City is skyscrapers that lack both efficiency and diversity,” he said. “We’re making the Green New Deal come alive with prehistoric buildings that use renewable materials.”

Wattle and daub is a composite material usually made of some combination of wet soil, clay, sand, animal dung and straw, although some architects also use hair, blood, and urine in the mixture.

“If someone wants to build one of those glass and steel monstrosities, they can apply for a permit but we’ll just deny it,” de Blasio said. “We need strong mandates that guarantee reduced emissions — and buildings that don’t switch to wattle and daub by 2030 will face fines of $1 million.”