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.
With more than 37 million speakers, Spanish is by far the most spoken non-English language in the U.S. today among people ages 5 and older. It is also one of the fastest-growing, with the number of speakers up 233% since 1980, when there were 11 million Spanish speakers.