Italian sources, from Sannazario, Ariosto, Guarini, Bojardo, and others.
Zicari who, it must be said, has made the best of his case, will have it
that the musterings and battles of the good and evil angels are copied
from the 'Angeleide' of Valvasone published at Milan in 1590. But G.
Polidori, who has reprinted the 'Angeleide' in his Italian version of
Milton (London, 1840), has gone into this matter and thinks otherwise.
These devil-and-angel combats were a popular theme at the time, and
there is no reason why the English poet should copy continental writers
in such descriptions, which necessarily have a common resemblance. The
Marquis Manso was very friendly with the poets Tasso and Marino, and it
is also to be remarked that entire passages in 'Paradise Lost' are
copied, _totidem verbis,_ from the writings of these two, Manso having
no doubt drawn Milton's attention to their beauties. In fact, I am
inclined to think that Manso's notorious enthusiasm for the _warlike_
epic of Tasso may first of all have diverted Milton from purely pastoral
ideals and inflamed him with the desire of accomplishing a similar feat,
whence the well-known lines in Milton's Latin verses to this friend,
which contain the first indication of such a design on his part. Even
the familiar invocation, 'Hail, wedded Love,' is bodily drawn from one
of Tasso's letters (see Newton's 'Milton,' 1773, vol. i, pp. 312, 313).

It has been customary to speak of these literary appropriations as
'imitations '; but whoever compares them with the originals will find
that many of them are more correctly termed translations. The case, from
a literary-moral point of view, is different as regards ancient writers,
and it is surely idle to accuse Milton, as has been done, of pilferings
from Aeschylus or Ovid. There is no such thing as robbing the classics.
They are our literary fathers, and what they have left behind them is
our common heritage; we may adapt, borrow, or steal from them as much as
will suit our purpose; to acknowledge such 'thefts' is sheer pedantry