Quotations from Chapter 11 of Edward Gibbon's History of the Decline and Fall of the Roman Empire ("Reign of Claudius — Defeat of the Goths — Victories, Triumph, and Death of Aurelian (268 - 275 A.D.)"):
Such, indeed, is the policy of civil war: severely to remember injuries, and to forget the most important services. Revenge is profitable, gratitude is expensive.
(see also Gibbon _-_Table_of_Contents, Gibbon_-_Thoughts_Upon_Reading, ... and http://www.his.com/~z/gibbon.html for a single-page presentation of Gibbon quotes)
(correlates: Gibbon - Table of Contents, GibbonChapter12, GoodRecovery, ...)