Debatably the rarest stamp error in U.S. history, the Inverted Jenny is among the most mythical. The plane depicted on the stamp is the JN-4HM, built by the Curtiss company in the middle of World War I (95 percent of U.S. pilots trained on JN-4s during WWI). Philately, like many other hobbies, enjoys the self-referential: this was the first plane used to deliver mail.

A printing error caused the blue vignette—the airplane and the air around it—to be printed upside down, while the red border framing the scene was printed correctly. The error only appeared on a single pane of 100 stamps, which has since been broken up, so that mostly single examples of the stamp exist, though there remain two blocks of four. In 2016, a single Inverted Jenny sold at auction for $1,351,250.

The Jennys—military biplanes—were modified for government airmail service with extra fuel tanks, a different engine, and a hopper for mail. They often crashed. In fact, the very first U.S. Post Office Department airmail flight on May 15, 1918, ended in disaster. The pilot flew in the wrong direction and crashed in a farmer’s field, ironically next to a property owned by Otto Praeger, the postmaster official in charge of airmail. “None of the first day’s mail made it,” says Scott Trepel, president of Siegel Auction House. “They had to send it the next day.”

The year 1847 is a huge one for stamps: this was the first year that you could purchase stamps from the United States government and affix them to a piece of mail as a method to prepay for its delivery (the legislation was passed in 1845). These are examples of the very first U.S. Federal stamps. Naturally, a great deal of correspondence was exchanged before 1847—the United States Post Office Department was established in 1792—but those letters were mostly paid for by the receiver.

Benjamin Franklin, who along with George Washington graced the first stamps, has a fascinating history with the post, filled with intrigue. In 1775, upon his return from England, Franklin was named postmaster general of the independent colonies by the Continental Congress. But long before, the Crown had named him postmaster general of the American colonies in 1753, a post he shared with William Hunter. Franklin was fired from that job when, in 1774, it was discovered that he had been opening mail (between English authorities) and feeding the correspondences’ contents to his rebel friends—in what’s become known as the Hutchinson Affair.

The Stamp Act, passed by the British Parliament in 1765, often cited as one of the immediate causes of the American Revolution, was, in fact, a tax. It was levied on American paper used for legal, official or everyday useful documents: ship’s papers, business licenses, calendars, declarations, inventory, etc. —even playing cards. The “stamp” was applied to paper to denote that the tax had been paid. While the money demanded by the act was quite low and the act was repealed the following year, the damage was done.

The colonies were incensed at the notion that they could be taxed by anyone outside their elected assemblies. Mob violence and intimidation followed, forcing stamp tax collectors to resign their positions and driving away ships carrying stamp papers at seaports. Colonial orators, like Patrick Henry, as well as newspapers, seized on the issue of English tyranny taking the form of taxation without representation, building the wave to revolution some 10 years later.

In the world of U.S. stamp collecting, the Blue Boy is akin to the Mona Lisa. Between 1845, when Congress established federally standardized rates for postage and 1847, when the first federal postage stamps were produced, postmasters in counties and cities within the 29 states issued their own provisional stamps. Postmasters got creative with the designs. For example, the St. Louis provisional stamps display the image of two bears holding the United States coat of arms between them.

Of particular interest are such provisional stamps from Alexandria, which was retroceded to the state of Virginia (from the District of Columbia) in these years. Seven such stamps are known to exist, but most of them are “buff” or a brownish-yellow color. Only one of them is bright blue—found on a love letter sent in 1847, that was supposed to be burned by its recipient—earning it the name “Blue Boy,” after the famous portrait—of a boy in fancy blue clothes—by English painter Thomas Gainsborough.

Stamp collectors love rarities, firsts and errors—and these stamps have all three, plus some politics. While the stamps were printed under President Ulysses S. Grant, their issue was conceived in 1868, during the fraught days after Andrew Johnson had been impeached, but still held on to power. Highly controversial and discontinued after one year, these were the first U.S. stamps printed using two colors.

They also denoted scenes, like Columbus’s arrival in America (previously stamps had only featured portraits). The pictorials are also the first example of a printing error by the Post Office Department. To print in more than one color, each color had to be printed separately; the careless placing of several sheets upside down in the press resulted in the first American invert errors.

When a four-stamp block of the 1869 Pictorials (24-cent inverts featuring John Turnbull’s painting, Declaration of Independence) was sold at auction in London in 1938, it attracted worldwide attention. It was the first time a transatlantic telephone line was used to purchase a lot at an auction.

In 1963, Life magazine said this stamp “Pound for pound, is the most valuable substance on earth.” The stamp dates back to 1851 when Hawaii was a sovereign nation and a popular destination for American missionaries spreading the gospel. Yet the Kingdom of Hawaii’s postmaster was American, and Honolulu’s and San Francisco’s post offices were well-connected. Collectors love these stamps for both the rarity of their survival, as well as their fanciful numerals.

Interestingly, the 2-cent stamp didn’t serve much of a purpose—the only use was for a newspaper or the captain’s fee (ship captains received 2 cents for every letter they carried). Audrey Hepburn fans will recognize a stamp similar to this one from her 1963 picture with Cary Grant, Charade, but there’s a catch. In that film, where a Hawaiian Missionary stamp plays a key part in the intrigue, its value is 3 cents, but there was no such thing as a 3-cent Missionary, only 2-cent, 5-cent and 13-cent.

This stamp offers a peek into the American mythos of “cowboys and Indians.” Established in 1860, the Pony Express was a private mail service using a network of young riders and stations wherein mail could travel from across the country in approximately 10 days (the alternative was stagecoach or ship). Its parent company, Central Overland California and Pike’s Peak Express Company, is stamped on this cover. One Express rider, traveling east through Nevada in 1860, disappeared. Two covers from his mailbag, which was recovered two years later, survive to this day and bear the handwritten words: “Recovered from a mail stolen by the Indians in 1860.”

For all the Pony Express’s legends (both Buffalo Bill Cody and Wild Bill Hickok claimed to be riders; there’s no evidence either was), the outfit lasted only 19 months and was, in fact, somewhat of a publicity stunt by three businessmen attempting to win a government mail contract.

Transportation was the key theme of the six commemorative stamps—featuring the bridge at Niagara Falls and a steam engine, among others—issued in 1901 to commemorate the Pan-American Exhibition held in Buffalo, NY. Because these stamps were printed in two colors, the opportunity was ripe for error, and pictorials on the sheets of the 1, 2 and 4-cent denominations were inverted.

The Pan-American Expo is less remembered for its stamps or Jumbo—the 9-ton elephant, a hero of Britain’s wars in Afghanistan (who turned on his owner and was later executed for it)— than for the assassination of President William McKinley on September 6. McKinley was shot twice at close range by anarchist Leon Czolgosz as he greeted admirers at the fair. He died from his injuries eight days later (his vice president, Teddy Roosevelt, had been so confident of the president’s recovery, he went camping in the Adirondacks).

They’re tricky, those CIA agents. Between 1975 and 1981, the Post Office released a series of Americana stamps, four of which depicted light sources.

Of these, a $1 stamp—depicting a colonial rush lamp and candle holder—was printed as an invert on a single pane of 100 stamps. In 1986, nine CIA agents who noticed the error purchased the pane with the 95 remaining stamps at the post office in McLean, Virginia (the post office had unknowingly sold the other five to be used as everyday postage).

The agents replaced the rare stamps with regular $1 issues, then sold a pane with 85 of the inverted rush lamp stamps (plus one damaged stamp) to a collector for $25,000. Each of the agents kept one stamp for themselves. A scandal soon followed, and the agency demanded that the agents return the stamps or face termination (they had been purchased with taxpayer money, after all).

Four agents returned their stamps, four quit or were terminated, and one agent claimed they had lost theirs and kept their job.

This stamp gets recognition not only because it’s an invert, but because it’s the last invert that the United States Post Office printed, back in 1992—on a stamp commemorating the 200th anniversary of the New York Stock Exchange (NYSE). Only 56 of these stamps are known to be in existence. Surrounded by a green border with red numerals, the inverted images include one scene of modern traders, depicted standing beneath a hub of monitors on the stock exchange, and an exterior view of the exchange’s neoclassical facade, at 11 Wall Street.

The NYSE was unofficially created on May 17, 1792, when 24 stock brokers signed the Buttonwood Agreement, which stated that the brokers could only trade with each other and that they were to earn a commission of 0.25 percent. It was signed outside 68 Wall Street, under a buttonwood tree. The agreement was reached after William Duer’s overzealous borrowing (and defaults) caused a financial panic earlier that year.