Dominoes are ancient gaming devices, similar to playing cards. Instead of numeric denominations such as those found on playing cards, dominoes are marked with different numbers of spots or "pips." These are meant to symbolize the combinations resulting from rolling a pair of six-sided dice. Invented in China originally, dominoes gradually made their way to Europe, where additional blank-sided dominoes increased the number of possible rolls as if rolling only one die, for example. Dominoes commonly sell in sets of 28, with the double-six being the largest number. Other sets include double-nines and even larger numbers. Today dominoes appear in many different materials, but hard plastic is the most common. A large foam-rubber set, however, allows for outdoor play and a safer version for young children.