Mathias and his lieutenant, Duke Mercury, to defend Low Hungary; the
second led by Ferdinand, the Archduke of Styria, and the Duke of
Mantua, his lieutenant, to regain Caniza; the third by Gonzago,
Governor of High Hungary, to join with Georgio Busca, to make an
absolute conquest of Transylvania.

In pursuance of this plan, Duke Mercury, with an army of thirty
thousand, whereof nearly ten thousand were French, besieged
Stowell-Weisenberg, otherwise called Alba Regalis, a place so strong
by art and nature that it was thought impregnable.

This stronghold, situated on the northeast of the Platen Sea, was,
like Caniza and Oberlympack, one of the Turkish advanced posts, by
means of which they pushed forward their operations from Buda on the
Danube.

This noble friend of Smith, the Duke of Mercury, whom Haylyn styles
Duke Mercurio, seems to have puzzled the biographers of Smith. In
fact, the name of "Mercury" has given a mythological air to Smith's
narration and aided to transfer it to the region of romance. He was,
however, as we have seen, identical with a historical character of
some importance, for the services he rendered to the Church of Rome,
and a commander of some considerable skill. He is no other than
Philip de Lorraine, Duc de Mercceur.'

[So far as I know, Dr. Edward Eggleston was the first to identify
him. There is a sketch of him in the "Biographie Universelle," and a
life with an account of his exploits in Hungary, entitled:
Histoire de Duc Mercoeur, par Bruseles de Montplain Champs, Cologne,
1689-97]