Forty Thieves Solitaire consists of four types of piles which are:
The Tableau: These are the 10 piles that make up the main table. Each consists of 4 cards, placed face-up.
The Foundations: These are the eight empty piles above the tableau piles.
The Stock: It is a single-pile that contains all the remaining cards placed face-down.
The Discard: It is a single-pile where the cards from the stock are dealt and placed face-up.
The objective of the Forty Thieves solitaire game is to move all the cards from the tableau and the stock onto the foundations, building 8 foundations(2 of each suit) from Aces all the way up to the Kings following the same suit.
Forty Thieves Solitaire is played using two decks of cards or 104 cards. Out of these, 40 cards are dealt face-up to the 10 tableau piles, with each pile having 4 cards.
The remaining cards are placed face-down in the single Stock pile.
Moving Cards Around the Tableau: Only one card can be moved at a time. The top card of each tableau pile can be moved to another tableau pile if it is one rank lower and of the same suit as the card it is being placed on. For example, you can move 8 of Hearts onto 9 of Hearts.
Moving Cards to the Foundations: Every foundation starts off with an Ace and all the way up to the King. You can move the cards onto the foundations if the card is one rank higher and of the same suit as the card it is being placed on. For example, You can place 2 on Aces, followed by 3, 4, and up to the King.
Drawing Cards from the Stock: The top card of the stock can be drawn and placed in the discard pile from where it can be either moved to the tableau or onto the foundation. It must follow the same rule i.e one rank lower and of the same suit as the card, it is being placed on.
Unlimited Undos: You can undo your every move as many times as you want to. The game offers unlimited undo and there is no restriction over how many times you can undo your moves, however, each undo will count as a new move.