Encyclopedia Britannica:

From its simplicity of form, the cross has been used both as a religious symbol and as an ornament, from the dawn of man's civilization. Various objects, dating from periods long anterior to the Christian era, have been found, marked with crosses of different designs, in almost every part of the old world. India, Syria, Persia and Egypt have all yielded numberless examples, while numerous instances, dating from the later Stone Age to Christian times, have been found in nearly every part of Europe.

Two of the forms of the pre-Christian cross which are perhaps most frequently met with are the tau cross, so named from its resemblance to the Greek capital letter T, and the svastika or fylfot, also called "Gammadion" owing to its form being that of four Greek capital letters gamma G placed together.
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