FACTBOX: Five facts about Pittsburgh, site of G20 meeting

(Reuters) - Pittsburgh, the erstwhile "Steel City," hosts the leaders of the Group of 20 leading rich and developing countries at a summit on Thursday and Friday.

Once covered in smog so thick that a journalist in the mid-19th century described Pittsburgh as "hell with its lid off," the city was chosen by President Barack Obama as a "bold example" of America's potential to build a new green economy.

Pittsburgh is banking its future on a cleaner economy -- one based on education, healthcare and innovation in green technology. Here are five facts about the city:

* Pittsburgh boasts that it is home to American firsts that include the first U.S. motion picture house (1905); the first drive-in gasoline station (1913) -- the world's first big commercial oil strikes took place along the Allegheny River; the Ferris Wheel, invented by a Pittsburgh-based engineer and erected in Chicago (1893); the beer-can pull tab (1962); and BigMac (1967).

The city also boasts many medical breakthroughs, perhaps most notably the first polio vaccine (1953), developed by Dr. Jonas E. Salk, a University of Pittsburgh researcher and professor.

* The city was named Pittsburgh in 1758 in honor of William Pitt the Elder, a British statesman who masterminded the military strategy that enabled the British to defeat the French in Pennsylvania during the Seven Years War.

* Sports-crazy Pittsburgh is home to the most recent champions in professional hockey and football, the Penguins and the Steelers, who have won the most Super Bowls, with six titles.

* Divided by three rivers -- the Monongahela, Allegheny and Ohio -- Pittsburgh has 446 bridges, and is so hilly it has more than 700 sets of public stairs, a number that some locals say is the most of any city in the country.

* A quirk of the local "Pittsburghese" dialect is the use of "yinz," a variation on the contraction "y'all," or "you all," which has earned Pittsburghers the nickname "Yinzers."

(Sources: Pittsburgh History & Landmarks Foundation, The Pittsburgh Speech and Society Project at Carnegie Mellon University, Senator John Heinz History Center, Reuters.)

(Compiled by Rebekah Kebede, Herb Lash and Patricia Zengerle)