As I understand it, string theory is the result of attempts by physicists to find a theory of everything. The strings in the theory are very small, have various shapes or forms, and are the basis of all sub-atomic particles and the basis of all energy, too.
That sounds a lot like "apeiron", a philosophical-physical abstract hypothesized by Anaximander. From Wikipaedia,
For Anaximander, the principle of things, the constituent of all substances, is nothing determined and not an element such as water in Thales' view. Neither is it something halfway between air and water, or between air and fire, thicker than air and fire, or more subtle than water and earth.[8] Anaximander argues that water cannot embrace all of the opposites found in nature — for example, water can only be wet, never dry — and therefore cannot be the one primary substance; nor could any of the other candidates. He postulated the apeiron as a substance that, although not directly perceptible to us, could explain the opposites he saw around him.
Also from Wikipaedia, on string theory,
String theory is a model of fundamental physics, whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point particles that form the basis for the standard model of particle physics. The phrase is often used as shorthand for Superstring theory, as well as related theories such as M-theory. By replacing the point-like particles with strings, an apparently consistent quantum theory of gravity emerges. Moreover, it may be possible to "unify" the known natural forces (gravitational, electromagnetic, weak nuclear and strong nuclear) by describing them with the same set of equations, as described in the Theory of everything.It is all well-beyond my comprehension, but they sound pretty similar to me.