Typical mistake: “The Battle of Hastings was of great historic importance.”
Historic means “memorable, important in history.” Examples: a historic occasion; historic buildings. So “great historic importance” is like saying “great important importance.”
Historical means “about history.” Examples: historical research; historical novels. So we can say “The battle was of great historical importance” (= very important in history). Historical also means “having really existed in the past” or “because of past events.” Example: Was Robin Hood a historical character?
Source: Ilson and Whitcut, Mastering English Usage, Prentice Hall, p. 75.
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