A history of the war between Athens and Sparta, along with both of their allies and colonies. The author was an Athenian citizen who tried not to take sides in his recording of events and avoided second hand stories as well as attributions of events to divine providence or fate. His writing is sometimes considered dry and dense compared to other ancient Greek historians of his time, and he has been called "the first modern historian" in contrast to historians such as Herodotus who came before him but were less factually rigorous.