On 1974, Watergate figure John Ehrlichman was sentenced to prison for his role in the break-in at the office of Daniel ...

But not the U.S. Mint. The modern successor to the early coin-striking center built on Seventh Street in 1792 is now the world’s largest coin-making factory.

Some quarters are much more valuable than 25 cents. Case in point: These 20 rare quarters are worth more than $7.5 million combined.

Williams noted that the current Mint -- there has been one in Philadelphia since 1792 -- was built during the Lyndon B. Johnson administration, when asbestos in buildings was prevalent.