Complex sentence: The library taken by the Earl was that of Dom Fernando Martins Mascarenhas, then Bishop of Faro, whose house Essex occupied during the raid: it is said to have included many of Osorio's books.
Split into simpler sentences: The library taken by the Earl was that of Dom Fernando Martins Mascarenhas, then Bishop of Faro, whose house Essex occupied during the raid. This is said to have included many of Osorio's books.