These eras are contrasted using research to validate.
As you differentiate among these three styles and eras, you might look at Romanesque and how art was influenced by "economic prosperity, relative political stability, and an increase in population" (http://www.metmuseum.org/toah/hd/rmsq/hd_rmsq.htm). This term is tricky since regional variations occurred throughout Europe. However, research finds that Romanesque "often refers to all works of this era, including the later Norman variations. The most recognizable feature of these buildings is there massiveness. In a general sense, it is easy to distinguish such structures from their more slender descendants in the Gothic era" (http://www.elore.com/Gothic/Learning/romanesque.htm).
As you explicate other key features, you might notice other traits. For example, "One of the most important structural developments of the Romanesque era was the vault. Originally intended as an alternative to fire prone wooden roofs, vaults became a major innovation in architectural features through the ensuing centuries" (http://www.elore.com/Gothic/Learning/romanesque.htm).
Romanesque, especially architecture of the eleventh and twelfth centuries, was distinguished by many factors. In sum, you might talk about how a dependence on Roman art is emphasized. This form also relied ...
The Romanesque and High to Late Gothic periods are briefly summarized.