Link Farms
Link farms are the SEO equivalent of cave painting.This primitive, but once highly effective, technique involved little more publishing a series of links on a page.
Though totally devoid of meaningful content, link farms were more than good enough for early search bots and web users alike. After all, this was well before the dawn of really sophisticated search engines so most folks were happy to find a collection of links that played their, uh, baser instincts.