Roman central heating worked slightly differently, but the goal was the same. A ground level furnace was used to create hot air which circulated beneath a thin floor raised up on pillars of tiles â this system was called a hypocaust. Not only was this central heating, it was underfloor heating! Smoke and fumes from the furnace were channelled off via flues so as not to pollute the heated space above. The same method was used to heat the waters in bath houses (yes, the Romans gave us hot baths too). Concrete. Opus caementicium (Roman concrete) was made from quicklime, pozzolana and an aggregate of pumice.
WHAT THEY MEAN: The most recent Census count (which dates to 2008) found the 227 million Americans above the age of five speaking only English at home. Another 55 million spoke 379 other languages.
Native North American languages are spoken by about 380,000 Americans, according to the 2000 census. The Navajo Nation numbers almost 300,000 people, of whom about 178,000 speak the Navajo language, making it the most widely spoken Native American language....