mid-15c., fertil, "bearing or producing abundantly," from Old French fertil (15c.) and directly from Latin fertilis "bearing in abundance, fruitful, productive," from ferre "to bear" (from PIE root *bher- (1) "to carry," also "to bear children"). Fertile Crescent (1914) was coined by U.S. archaeologist James H. Breasted (1865-1935) of University of Chicago in "Outlines of European History," Part I.
word-forming element used to make verbs, Middle English -isen, from Old French -iser/-izer, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.
The variation of -ize and -ise began in Old French and Middle English, perhaps aided by a few words (such as surprise, see below) where the ending is French or Latin, not Greek. With the classical revival, English partially reverted to the correct Greek -z- spelling from late 16c. But the 1694 edition of the authoritative French Academy dictionary standardized the spellings as -s-, which influenced English.
In Britain, despite the opposition to it (at least formerly) of OED, Encyclopaedia Britannica, the Times of London, and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (such as advertise, devise, surprise). American English has always favored -ize. The spelling variation involves about 200 English verbs.