To paraphrase an infomercial, "I dunno, it just writes itself!" Tamora and Titus are almost perfect duplicates, and the more they change, the more they stay the same. In Act III, we get to see how Titus responds to the wrongful execution of his sons. And what does he say? Oh, it's too much!

Check this out:

Titus: Hear me, grave fathers! noble tribunes, stay! (Act 3)
Tamora: Stay, Roman brethen!--Gracious conqueror, Victorious Titus (Act 1)

Even if we ignore the word similarity, the syntax is nigh on identical! I'm going to go ahead and make a great big faux pas and speculate on authorial intent. Shakespeare is almost certainly going out of his way to show us that the difference between the civilized and the uncivilized, the male and the female, heck even reality and lies (referring to my last blog post) is just a matter of perspective and the ability to enforce that perspective.

In more words, Titus is a Roman warrior of incredible skill and great age, while Tamora is a barbarian Queen of great beauty and cunning mind. Yet despite their different backgrounds, they couldn't possibly be more similar. Were I to make a movie out of this, I'd have a single actor play both parts.