Various - Notes and Queries, Number 203, September 17, 1853 стр 5.

In foreign words like Alcides, no change ever took place; it was the same for all numbers and cases, and the explanation was left to the context. Here are a couple of examples from Shakspeare himself:

"To Brutus, to Cassius. Burn all. Some to Decius house, and some to Cascas; some to Ligarius. Away! go!"Julius Cæsar, Act III. Sc. 3.

All here are genitives, as well as Cascas. If any doubt, Brutus and Cassius, we have just been told, "Are rid like madmen through the gates of Rome," so they