Eckler states that the modern history of word squares (following in the footsteps of the SATOR square) started with the following one, published in 1859:
Here's a six-square:
And then he goes on to discuss word cubes! An n-cube contains n words repeated three times each and n(n-1)/2 words used six times each, it has a total of 3n^2 words. And yes, people have extended the idea to hypercubes.
Get dozens of book recommendations delivered straight to your inbox every Thursday.