It's easy to forget when you're playing your millionth game of computer solitaire, but the standard pack of playing cards is an ancient and mysterious object.

Decks of cards have been used in China since the 600s, and gradually spread to Egypt. The standard deck of Egypt's Mamluk dynasty, with swords, batons, cups and coins, eventually traveled into Italy and later the rest of Europe.

While some countries like Italy and Greece still use the original Egyptian card suits, most decks have adopted the four French suits that evolved in the late 1400s. There's no exact origin for the designs, but each suit is connected to a distinct part of society:

• Clubs are associated with peasants, laborers and work.
• Diamonds are connected to merchants and wealth.
• Hearts are usually compared to the clergy, and the search for happiness and love.
• Spades are tied to warriors and also nobility.

The French also gave us another very familiar part of the modern deck: the aces.

While a "one" card has always existed, the French Revolution, which saw the French people overthrow their King and Queen, turned the lowly ace into a "trump" card that could defeat the King and Queen cards.

But it turns out even the number of cards in a deck has a special meaning.

The more you dig into the numbers in a standard deck of cards, the more freaky coincidences with the calendar you notice.

Start by adding up all the cards (count Jacks as 11s, Queens as 12, and Kings as 13). We did the math for you: the pack adds up to 364. Add in a Joker for good measure and you get 365, or the number of days in a year.

Not counting Jokers, there are 52 cards in a deck, just as there are 52 weeks in a year. Finally, each suit has 13 cards. While we normally think of 13 as an unlucky number, it once had another, more important meaning.

Lunar calendars, which were used by many older societies and are still tracked by some cultures today, include a smaller 13th month to account for the moon's 12.4 rotations around the Earth. That means the number of cards in a suit lines up with the "13 months" in a lunar year.

Finally, the Joker often gets a bad rap as a symbol of evil or chance haunting the deck, but there's a simple explanation for this wild card.

The card came about in America during the 1860s, when Euchre players needed a special trump card for their game. Early trump (or bower) cards were sometimes called Jukers, because the name Euchre comes from the German word Juckerspiel.

Eventually, the grinning Joker design caught on, and the rest is history.

Did you know these secrets about the deck of cards?