How have historians recovered parts of Polybius’s lost books?

While Polybius’s The Histories originally consisted of 40 books, only the first five are extant in their entirety. Much of the remainder of his work has been recovered through various excerpts preserved in collections of passages from Greek historians. These collections were assembled in the 10th century and were subsequently rediscovered and published by various editors between the 16th and 19th centuries.1