Monoliths are machines built by an unseen extraterrestrial species whom Clarke dubbed the Firstborn and whom he suggests are the earliest highly intelligent species to evolve in the Milky Way. In the series of novels (and the films based on these), three Monoliths are discovered in the Solar System by Australopithecines and their human descendants. The response of the characters to their discovery drives the plot of the series. It also influences the fictional history of the series, particularly by encouraging humanity to progress with technological development.The first Monolith appears at the beginning of the story, set four million years before the present era. It is discovered by a group of Australopithecines and somehow triggers a considerable shift in evolution, starting with the ability to use tools and weaponry. It is later revealed that thousands of other Monoliths exist elsewhere in the galaxy.