Thucydides tells us (i. 22. 2 f.) his procedure in respect of what he calls . He claims not to have obtained information ‘from anyone who happened to be available’ but to have described events of which he himself was a witness and, for the rest, to have scrutinized his information with the utmost care. This was a laborious process, since accounts were often contradictory; memory has gaps, and a man’s picture of a past event is coloured by his loyalties (i. 22. 3). Documentation of the kind which a modern historian would expect to use was hardly available to Thucydides. Treaties were recorded in writing, and so were Athenian decrees and some balance-sheets; but it is questionable whether the letter written by Nicias in 414 (vii. 8, 10–15) was kept in an archive long enough for Thucydides to read it, and the figures given in iii. 87. 3 for cavalry and hoplite deaths in the plague were probably taken from a speech made by a general in the assembly. There is no evidence for the existence in the fifth century of written operation orders, situation reports, or war diaries, and it is to be presumed that what Thucydides has to tell us about operations is based on oral information from people who had taken part or had themselves received information from participants.