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.
According to the 1990 census, 94% of the U.S. population speak only English. Adding those who speak English well or very well brings this figure to 96%. Only 0.8% speak no English at all as compared with 3.6% in 1890.