A marble was a small round toy.

A Dogon's sixth eye resembled a blue marble. (TV: Random Shoes ^[+]Jacquetta May, Torchwood series 1 (BBC Three, 2006).)

On Go-Ray, the First Doctor, John and Gillian escaped from some Go-Rays when the Doctor scattered John's marbles on the ground, causing the Go-Rays to slip and fall. (COMIC: Enter: The Go-Ray ^[+]Bill Mevin, TVC comic stories (1965).)

When the Second Doctor visited the Panjistri homeworld, he had a bag of glass marbles in his pocket. (PROSE: Timewyrm: Apocalypse ^[+]Nigel Robinson, Virgin New Adventures (Virgin Books, 1991).)

As a child, Ace once lost a white marble in the school playground; when she found it weeks later, it was scuffed and cracked. (PROSE: Lucifer Rising ^[+]Jim Mortimore and Andy Lane, Virgin New Adventures (Virgin Books, 1993).)

Amy and Rory escaped from a Sontaran ship in 1605 by firing marbles from a slingshot at the Sontarans' probic vents. (GAME: The Gunpowder Plot ^[+]Phil Ford, The Adventure Games (BBC Wales Interactive, 2011).)

While aboard the HMS Thunder in 1941, the Seventh Doctor removed several marbles from his pocket. (AUDIO: Dark Convoy ^[+]Error: Code 2 - no data stored in variables, cache or SMW.)

Martin Donaldson initially confused the Elgin Marbles for giant versions of the toy. (AUDIO: A Life in the Day)