This essay examines shifting representations of the asidhārāvrata (lit. "sword's edge observance") across a range of Sanskrit literary and religious texts. Originally a Brāhmaṇical ascetic discipline, an observance (vrata) by this name is the earliest ritual involving sexual contact documented in the corpus of śaiva tantras. In its tantric adaptation, an orthodox practice for the cultivation of sensory restraint was transformed into a means for supernatural attainment (siddhi). Diachronic study of the observance in three early Śaiva texts – the Niśvāsatattvasaṃhitā, Mataṅgapārameśvara, and Brahmayāmala – reveals changes in ritual emphases, women's roles, and the nature of engagement in eroticism. Analysis of the asidhārāvrata thus sheds light on the early history of tantric sexual rituals, which by the end of the first millennium had become highly diverse. It is argued that the observance became increasingly obsolete with the rise of Śaiva sexual practices more magical, ecstatic, or gnostic in orientation.