Niobe and Amphion had fourteen children (the Niobids), and in a moment of arrogance, Niobe bragged about her seven sons and seven daughters at a ceremony in honor of Leto, the daughter of the titans Coeus and Phoebe. She mocked Leto, who only had two children, Apollo, god of prophecy and music, and Artemis, virgin goddess of the wild. Leto did not take the insult lightly, and in retaliation, sent Apollo and Artemis to earth to slaughter all of Niobe's children. Apollo killed the seven sons while they practiced their athletics. The last son begged to be spared, but the arrow had already left Apollo's bow, and the boy was struck dead. Artemis killed the seven daughters with her lethal arrows. (Some versions have a few of the children being spared.)
At the sight of his dead sons, Amphion either committed suicide or was also killed by Apollo for wanting to avenge his children's deaths. In any event, Niobe's entire family was dead in a matter of minutes. In shock, she cradled the youngest daughter in her arms, then fled to Mt. Siplyon in Asia Minor. There she turned to stone and from the rock formed a stream (the Achelous) from her ceaseless tears. She became the symbol of eternal mourning. Niobe's children were left unburied for nine days because Zeus had turned all of the people of Thebes into stone. Only on the tenth day did the gods have pity and entomb her children.
Niobe is weeping even to this day. Carved on a rock cliff on Mt Sipylus is the fading image of a female that the Greeks claim is Niobe (it was probably Cybele, the great mother-goddess of Asia Minor originally). Composed of porous limestone, the stone appears to weep as the water after a rain seeps through it
This myth vividly illustrates the vicious nature of the gods. Often, the gods would strike deadly revenge on mortals merely for acting on human weaknesses. Leto had Niobe's entire family killed because of an arrogant comment. This theme of deadly revenge is common in myths of Artemis and Apollo. For example, Artemis turns Actaeon into a stag which his hunting dogs devour because he accidentally saw her naked after a bath. Apollo is as equally unforgiving. He took lethal action against the mortal Marsyas after Marsyas challenged Apollo to a contest of music and lost. Apollo skinned him alive. Clearly, the myth of Niobe demonstrates the wrath of both Apollo and Artemis and is a warning to mortals not to compare themselves to the gods.