Rhea was sad because she loved her children , so when Zeus was born , Rhea gave a stone instead of Zeus for Cronus to swallow . But when Zeus was about to be born , Rhea sought Gaia to devise a plan to save him , so that Cronus would get his retribution for his acts against Uranus and his own children . Rhea gave birth to Zeus in Crete , handing Cronus a rock wrapped in swaddling clothes , which he promptly swallowed .