Situated prominently within the expansive paved courtyard of the Eleusinian sanctuary, the temple of Artemis Propylaea and Poseidon Patroos greets worshippers as they approach from the Sacred Way, standing to their right. Its existence first comes to light through the writings of Pausanias, who notes its dedication. The temple’s names, “Propylaea” and “Patroos”, signify its placement near the gate and the Eleusinians’ veneration of Poseidon respectively. Regarding its construction date, it certainly predates 160 AD, when seen by Pausanias.
Remarkably, the temple’s foundation, crafted to support the structure of Pentelic marble, has remained intact. The temple featured a wooden roof overlaid with clay tiles, with porticos at both its front and rear. The supporting Doric columns, carved from a single block of stone, likely due to their modest size, provide structural elegance. In terms of size, the temple’s scale is comparable to that of the Acropolis’s Temple of Athena Nike.
Two altars were positioned near the temple: one just metres from the eastern entrance, and the other towards the northeast. Dedicated to the dual deities, these altars facilitated the worshippers’ religious practices, allowing them to offer devotions externally, reserving temple entry primarily for admiring the esteemed statues. The specific dedications of these altars remain unclear, although it is hypothesised that the eastern one was devoted to Artemis. This altar, adorned externally with limestone, was internally constructed using lime mortar and stone. In contrast, the altar presumably dedicated to Poseidon has deteriorated significantly over time.
Due to the fact that the orientation of the building is not aligned with that of the Great Propylaea, although they belong to the same building program, it is believed that the sanctuary was built on top of an older temple. There is also the possibility that this deviation was conscious, so that both sides of the sanctuary would be visible to those arriving at the courtyard of the Eleusinian shrine.