Niobe's fall is triggered by a single comparison spoken in pride at a festival honoring Leto, mother of Apollo and Artemis. Niobe, queen of Thebes and mother by her own count of fourteen children, seven sons and seven daughters in the fullest version of the story, though other sources give smaller and unequal numbers, argues publicly that she deserves greater honor than a goddess who has borne only two. The remark reaches Leto directly, and Leto sends her own son and daughter, both already armed and dangerous archers in their own right, to punish the insult rather than answering it herself.
Apollo kills Niobe's sons first, cutting them down one after another as they exercise or hunt, seemingly without warning, and Artemis kills the daughters as they gather to mourn their brothers, so that Niobe loses her entire family within what the sources treat as a single continuous massacre rather than a drawn out siege. Ovid's Metamorphoses gives the fullest surviving account of the killings themselves, lingering on each child's death in turn to build the scale of Niobe's loss before turning to her reaction.