Dated History: The manual states Mona the model in the Leonardo da Vinci mission was a fictional character and the inspiration for the painting, let alone whether or not Leonardo actually used a model for the creation of the Mona Lisa, was (at the time) unknown. In 2005, it was discovered that the Mona Lisa depicts Lisa del Giocondo, meaning the game was actually right to depict her as a real person (note that the "Mona" is a title, not part of her name — "Mona Lisa" is the Italian equivalent of "Madam Lisa"). Of course, the depiction of her as a surly model posing for Leonardo is still completely fanciful, especially considering he spent years working on it.
One third (six out of eighteen) of the cases take place during the one hundred fifty years between 1450 and 1600, roughly corresponding to The Renaissance. This is the largest number of cases clustered so close to each other in time.
The Middle Ages (c. 500 - 1500) is the most represented historical era in the game, covering cases three through ten. However, the Middle Ages is a period in European history and five of those eight cases don't actually feature any portion set in Europe and three out of eight don't include Europeans in any way.
When you hover your cursor over a character you can speak to, text appears which normally reads, "Talk to [character name]". When you do this with Julius Caesar, the text instead reads, "Hail Caesar". The actual talking to Caesar is the same as for any other character, however.
The game takes you from 1490 B.C.E. to 1961, covering a span of 3,451 years. The first three cases represent over seventy-two percent of that time span. This means over eighty-three percent of the game takes place during less than twenty-eight percent of the time span it covers.