The Altar of the Twelve Gods (ΒΩΜΟΣ ΔΩΔΕΚΑ ΘΕΩΝ) was constructed in the Athenian Agora, NW of the Acropolis, at the direction of Pisistratos the Younger, Archon of Athens, 522/521 BC (Thucydides). In 1934, archaeologists excavated a marble statue base in situ next to a rectangular limestone hypaethral edifice on the Panathenaic Way. Its inscription reads “Leagros, the son of Glaukon, made the dedication / To the Twelve Gods”. Although the Altar is now buried under the Athens-Piraeus railway tracks, the author surveyed the exposed SW corner (12 September 2017) with a Gurley 20” theodolite (for solar observations) to Ground Truth published (magnetic compass) azimuths. This paper presents counter-evidence rejecting the interpretation that the Altar takes its orientation from the Panathenaic Way (Camp, 1986). Rather, the axis of the Altar’s peribolus wall openings is oriented to horizon points consistent with Graeco-Roman hypaethral astro-architectural design principles (Vitruvius), viz.: Full Moon rise nearest the Midwinter Minor Standstill (+18.66° decl.) and set nearest the Equinox Minor Standstill (-5.1° decl.). The significance of these lunar standstill alignments is that they connote systematic local and long-term luni-solar observations in the century preceding the 19-year luni-solar cycle proposed by Meton of Athens (ca. 432 BC): i.e., the NE peribolus opening framed the last of a series of Midwinter Lunar Eclipses observable in Athens every 19-years, viz.: Partial Eclipse 29 December 560 BC; Total Eclipse 29 December 541 BC; and Partial Eclipse 30 December 522 BC— this last coinciding with the Altar’s construction under Pisistratos the Younger.