The term comes from the Latin cento, a cloak made of patches; and that from the Greek κέντρων (gen. κέντρωνος). The Roman soldiers used these centones, or old stuffs patched over each other, to guard themselves from the strokes of their enemies. Others say, that centos were probably used for the patches of leather, etc., with which their galleries or screens, called vineae, were covered; under which the besiegers made their approaches towards any place. Hence centonarii, the people whose business was to prepare these centos.
The above quote is from Wikipedia