As the book opens, Indy and Assistant Professor Thornton are visiting Aigues-Mortes, France. As Thornton says, Aigues-Mortes translates as "dead water" in French. The town is named for the marshland that is all around it and it has never had potable water.

    As Thornton states on page 10, Aigues-Mortes is known for viticulture and salt production.

Professor Jones' most prized assistant at this time is Assistant Professor Thornton N. Thornton VI, while Professor Jones is Thornton's hero.

On page 7, Indy muses on the trek he and Thornton took to get to Aigues-Mortes, from his home in Utah, to New York, the voyage across the Atlantic, the train trip from Le Havre to Paris and south to Arles, before taking a carriage to the small town.

Aigues-Mortes was built by France's King Louis IX in 1240 to serve as a port for transporting troops to the Holy Land during the Crusades.

Page 14 reveals that Indy's father had a fair stash of money saved from an inheritance he had received from a dead uncle who once struck gold in the California gold rush.

On page 15, Thornton explains to Indy that historians don't deal with "treasure", but rather with old and humdrum official documents, like bills of sale or land grants, gathering little bits of data, like ants working endlessly to put together a better picture of the past. Indy thinks, Speak for yourself, and how he'd be more like a big game hunter tracking down prize finds in faraway places. This is a pretty good summation of real historians and Indy's later brand of "archaeology" in his illustrious career.

Indy and Thornton encounter Gypsies in France throughout the novel. Gypsies are a nomadic ethnicity living mostly in Europe, now more properly called the Romani. The term "gypsy" is seen as pejorative by the affected population. As explained by Stefan in Chapter 8, the term "gypsy" was short for "Egyptian", as the population was believed by Europeans to have immigrated from Egypt, though their true origin is not known, even by themselves; modern research into Romani genetics and language hints at an Indian origin.

The Gypsy Sarah tells Thornton she will be in Saintes-Maries with her people if he wants to come by to have a tarot card reading. Saintes-Maries-de-la-Mer is a town on the south coast of France, about 18 miles from Aigues-Mortes.

On page 30, Thornton tells Indy that King Louis IX died in Tunis of the plague during his second Crusade. But, he actually died in an epidemic of dysentery that was sweeping his army.

Thornton tells Indy he had once been an Eagle Scout. Eagle Scout is the highest attainable rank in the Boy Scouts of America (now Scouts BSA).

In Chapter 6, Thornton and Indy rent a Renault automobile in order to get to Saintes-Maries. Indy is the driver because Thornton does not know how to drive and Indy's been learning to drive his father's Ford Model T back home.

On page 42, Thornton and Indy come across some gardians herding cattle on white horses. As Thornton explains, a lot of cattle ranching is done in the Camargue delta, where Aigues-Mortes and Saintes-Maries are located. The white horses they ride are called Camargue horses.

Page 47 makes the claim that Indy grew up in the West, referring to the western United States. But it's a stretch to say he grew up there. As the later Young Indiana Jones Chronicles TV series depicts, he was born in New Jersey and lived there until he was 13, when his father moved the two of them to Utah in June 1912 after the death of Indy's mother.

On page 50, Thornton reads from his guidebook that Saintes-Maries was supposedly named for three Marys who arrived there on a boat from the Holy Land. In the real world mythology of the town, the three Marys were supposedly Mary Magdalene, Mary Salome, and Mary of Clopas, the three Marys who discovered that Jesus' tomb was empty after his resurrection. And, as Thornton also reads from the guidebook, a woman who was a servant to one of the Marys is said to have been named Sarah. This is the Saint Sarah who is considered to be the patron saint of the Romani people and they make frequent pilgrimages to Saintes-Maries-de-la-Mer to venerate her. Some fringe theorists have speculated that Sarah was the daughter of Mary Magdalene and Jesus Christ.

Indy seems to be skeptical of love throughout the book, seeming to forget that he fell in love with Princess Sophie when he was 9 in "The Perils of Cupid" and had a youthful romance with Norma Bellini in The Metropolitan Violin and The Bermuda Triangle.

On page 55, a menacing pair of Gypsies refer to Indy and Thornton as gorgios, i.e. outsiders. Gorgio is a Romani term for "outsider". 

As Chapter 9 opens, Sarah reads a tarot spread to see what is awaiting herself, Thornton, and Indy back in Aigues-Mortes. She shuffles the tarot deck seven times and lays ten cards out in a pyramid form. In tarot (and, in fact, most card games), seven is considered the smallest number of shuffles to truly mix a deck of cards. The number 7 is also important in numerology. A spread of ten cards in a pyramid form is called a Petit Lenormand (diagram at right). It is said to show the root cause of a problem, layer-by-layer, starting from the longer row to the tip. This is how Sarah performs the reading in the novel.

The French name of Gitans given to the Romani as stated on page 83 is correct.

The first clue in the ancient manuscript of Louis IX is to start at the Constance Tower. Historically, this is a tower started by Louis in 1242 and completed in 1254. 

On page 87, the treasure hunters follow a series of royal iris symbols (the fleur-de-lis) in a room of the Constance Tower. The symbol has been associated with the kings of France since Louis VI in the 12th Century. (Fleur-de-lis image from Wikipedia by Frater5, shared under the GNU Free Documentation License. Image modified here with a white background.)

    The man in the iron mask takes Indy and his friends to the Old Port in Marseille. As Sarah states here, the Canebière, Marseille's major street, leads into Old Port and, at the time of this story, Old Port was known for crime.

    Thornton remarks that Marseille is the third-largest city in France. I've been unable to confirm if that was true at the time of this story. It is currently the second largest.

The man in the iron mask plans to execute Indy and his friends by guillotine. He says the device was named for its inventor, Dr. Guillotin. Dr. Joseph-Ignace Guillotin (1748-1814) did not invent the device, despite popular belief that he did; he was an advocate to King Louis XVI in 1789 that executions should be performed in a quick and painless way, unlike many of the main forms of execution used at the time. The actual inventors were French physiologist Antoine Louis with German engineer Tobias Schmidt.

The man in the iron mask tells Indy and his friends that the antique guillotine he has obtained removed the heads of the greatest aristocrats in France during the Revolution. The French Revolution was a period of social and political upheaval in France from 1789-1799 which eventually led to republican democracy in the country and which spread and inspired citizens of other nations around the world to overthrow or replace monarchies and dictatorships.

   In Chapter 14, the man in the iron mask points out the Château d'If on a small island immediately off the Marseille coast. Thornton then remarks that the Château d'If was a prison where the historical Man in the Iron Mask had been held. Château d'If was an actual prison and former fortress built in the 16th Century on the Île d'If. Though there was an unidentified historical figure who has become known as the Man in the Iron Mask, he was never held at Château d'If, but at several other prisons over his 34-year incarceration (the mask worn by the prisoner was actually black velvet, misreported as iron by Voltaire).

    The part of the Man in the Iron Mask legend that Thornton relates, about his possibly being the twin brother of King Louis XIV, is from Alexandres Dumas' 1847 novel The Vicomte of Bragelonne: Ten Years Later, part three of which was titled The Man in the Iron Mask.

The man in the iron mask says that the German kaiser wants to help him, a fellow king, regain control of France, and already has plans for a war that will destroy Europe's foolish notion of the people voting for their leaders. He is referring to Kaiser Wilhelm II (1859-1941), ruler of Germany from 1888-1918. The kaiser did have grandiose plans for German dominance in Europe and they led, not entirely intentionally, to WWI, which began a couple months after this story.

At the end of the book, the Historical Notes section talks about the Romany's, the Man in the Iron Mask, and Marseille. Then the final paragraph fills the reader in that Thornton N. Thornton VI never published his research on Romany culture, much to the disappointment of Professor Jones, but not to Indy, who supports the Romany desire for privacy about their culture.