Turtles all the way down” is an expression of the problem of infinite regress. The saying alludes to the mythological idea of a World Turtle that supports a flat Earth on its back. It suggests that this turtle rests on the back of an even larger turtle, which itself is part of a column of increasingly larger turtles that continues indefinitely.

The exact origin of the phrase is uncertain. In the form “rocks all the way down”, the saying appears as early as 1838.[1] References to the saying’s mythological antecedents, the World Turtle and its counterpart the World Elephant, were made by a number of authors in the 17th and 18th centuries.[2][3]

The expression has been used to illustrate problems such as the regress argument in epistemology.