Angularity, as with a square stone, is a characteristic of the past versus roundness, the wheel, as a symbol of the future.

The modernist architecture of the last century (1930-1960) was an architectural movement or architectural style based upon a functionalist idea with an embrace of minimalism and a rejection of ornament. The use of round shapes was a style characteristic. It was a radical break with the past and a view to the future.

De La Warr Pavilion, Bexhill. 1935, Architect/Designer: Mendelsohn & Chermayeff. Source: http://flickr.com/photo/53921762@N00/1986171763

In images depicting the future, futuristic planes etc. the artists show a preference for round shapes.

Artist Tim Hildebrandt painted the rounded buildings of his future city yellow. Underneath the future he draws the angular past in a roman temple architecture. The man in the foreground points to the right, where the future lies.

(Michiels, I. editorial)