Clio was born among the nine Muses, daughters of Zeus and Mnemosyne, Memory. Hesiod names the nine as Clio, Euterpe, Thalia, Melpomene, Terpsichore, Erato, Polyhymnia, Urania and Calliope, with Calliope described as chiefest. Hesiod does not assign Clio the specialist title 'Muse of History'. That division of the sisters into distinct arts developed later, when Clio's name and association with fame made her a natural patroness of history and historical memory.

The oldest epic of Greece is a machine for making fame. It begins by begging a goddess to sing of the wrath of Achilles, the hero whose choice shortened his life and lengthened his glory, and it pauses in the middle of its account of the armies at Troy to make a frank confession: the poet himself knows nothing at first hand, for he hears only rumour, while the Muses, who are present at all things and forget nothing, could tell the name of every man who came to the war. Clio is the Muse of that confidence. Her sphere was never song alone but the preservation of whatever song proclaimed: the names, the lineages, the speeches, the boasts, all the cargo of the past that a people either carries or loses. Later ages, looking back at the habit, understood why she had been born the daughter of Memory. History is public memory taught to last, and the Proclaimer is its natural keeper. When Greek and Roman artists came to carve and paint her, they gave her the tools of the trade: an open scroll across her knees, a chest of books beside her, and sometimes a small trumpet, as if her proclamations might still be heard down the street.

Clio once laughed at the wrong goddess, and the story of what followed belongs to her alone. Aphrodite, the golden goddess of love, was wild with grief for Adonis, the beautiful youth who had been gored to death by a wild boar while hunting, and she roamed the hills crying his name. Clio mocked her: a goddess before whom kings and cities bowed, undone by the death of one pretty boy. Aphrodite could not strike a daughter of Zeus dead, so she aimed a subtler shaft. She made Clio burn with the same helpless, undignified passion for a mortal, Pierus, a king of Macedon, the mountainous land north of Greece. Clio lay with him and bore him a son, Hyacinthus, a boy so beautiful that every account agrees the world had never made a lovelier. Other tellers make Hyacinthus the son of Amyclas, a king of Sparta, but every telling agrees on what happened to him. Apollo, the god of music and light, loved him above all mortals, and one day at the discus ground the god hurled the heavy disc high into the air, and Hyacinthus, running forward to mark the throw, was struck on the head as it fell and died in Apollo's arms. The god would not let the boy vanish entirely. From the blood that soaked the earth sprang a new flower, dark, fragrant, and marked with the letters of a cry of grief, the hyacinth that still carries his name. Clio's mockery of love ended in a flower and in one of the oldest sorrows in the gods' catalogue of loves.

The child of Clio's punishment had an admirer before he had a grave. Thamyris, a bard of Thrace, the rough country beyond the north Aegean, was the son of Philammon, a famous minstrel, and he is remembered as the first man ever to love another male, his heart kindled by the beauty of Hyacinthus. His skill was equal to his passion, and there lay his ruin. Travelling through Messenia, the south-western region of the Peloponnese, the great peninsula of southern Greece, Thamyris came to the town of Dorion and boasted in the drinking hall that he would win any singing contest, even if the Muses themselves dared to stand against him. The nine sisters accepted the challenge at once, and they sang, and his claim collapsed before them. For his insolence they struck him blind where he stood, drained the heavenly sweetness out of his voice, and left him unable even to remember how to finger the lyre. The oldest epic remembers him in a single grim passage as a warning nailed above every bard's door: the singer who challenged the daughters of Memory lost his eyes, his song, and his name, and wandered the roads as a beggar. It was Clio's clearest lesson. She who proclaims fame also decides when fame is withheld, and no mortal voice outlasts the goddesses who keep the record.

Greek prose historiography developed in the fifth century BCE through writers such as Herodotus and Thucydides, but it is too strong to say that these earliest historians already worked under a formally established Clio as their exclusive patroness. The later classification of the nine Muses gave history to Clio, and Greco-Roman art then represented her with scrolls or books. The association is therefore genuine and ancient, but later than the simple Muse catalogue in Hesiod.

Clio shared the sanctuaries and cult of the Muses as a group. Mount Helicon in Boeotia became one of their most famous landscapes, while Apollo and the Muses were also connected with Delphi and later literary tradition associated them strongly with Parnassus. The Mouseion at Alexandria likewise took its name from the Muses collectively. These institutions belong to the broad cultural history of the Muses, not to a separate cult of Clio alone.

Clio's name still circles above the world. In 1865 the German astronomer Robert Luther, mapping the small planets between Mars and Jupiter, named one of them 84 Klio in her honour, a dark mass of rock and ice carrying the Muse of history around the sun roughly every four and a half years. In the twentieth century scholars coined cliometrics, the discipline that weighs the past with statistics and economic models, and they named it for her outright. Statisticians, archivists, librarians, genealogists, and every schoolchild who has ever had to memorise a date all work, knowingly or not, in her province. She never demanded worship in return. She asked only that the record be kept. From the nine nights at Olympus to a telescope's eyepiece, Clio remains the Proclaimer, the voice that insists the past happened and will not be unremembered.