The altar in the north porch was one to Zeus and its presence there suggests the reasonable theory that the marks in the rock below it and the square hole in the roof above are a memorial of the thunderbolt which he hurled at Erechtheus according to Hyginus (Fab., 46). Cf. Petersen, op. cit., p. 72. One cannot say which is the earlier tradition, that preserved in Hyginus or that in Euripides (Ion, 281) according to which πληγαὶ τριαίνης thrust Erechtheus into a χάσμα χθονός (Furtwängler, Masterpieces, p. 436, note 3). There was a tradition that Zeus, at the request of Poseidon, killed Erechtheus with a thunderbolt, a tradition which becomes the more interesting in the light of an inscription found on the Acropolis (Lolling, Δελ. Ἀρχ., 1890, p. 144) which proves that an ἄβατον Διὸς Καταιβάτου existed there. The stone bearing the inscription was found in a mediaeval wall north of the northeast corner of the Parthenon. Three surfaces of the fragment are preserved showing that it came from a corner perhaps of a low wall enclosing the ἄβατον. One side of the block which is Pentelic marble is finely polished. There are no dowel or clamp-holes preserved and it is impossible to recover the dimensions of the original block. The face which bears the inscription of the late fourth century seems to have been redressed, since chisel marks are evident. The inscription may then have been recut. It is tentatively suggested that this fragment was part of the curb about the opening in the floor of the north porch.
Zeus hurled a thunderbolt which destroyed the chamber of Semele at Thebes and the place was an ἄβατον in the time of Pausanias (IX, 12, 4). When Zeus struck Erechtheus with a thunderbolt, the spot on the Acropolis where the lightning struck may likewise have become an ἄβατον. It is interesting to note that at Olympia, Pausanias (V, 14, 7) saw the foundations of the house of Oenomaus and two altars, one to Zeus Herkeios which Oenomaus seems to have built, the other to Zeus Keraunos erected later, after the thunderbolt had destroyed the house. The persons and palaces of mythical kings appear to have been a favorite mark for the thunderbolt of Zeus. The tradition preserved in Hyginus is an illustration, and tempts one to seek in the vicinity of the Erechtheum for some record of the thunderbolt.
And so too does the notice of the scholiast (after Apollodorus) on Sophocles, Oed. Col., 705, who says that near the Academy there was an altar to Zeus Kataibates who was also called Morios: ἐστὶν ὅ τε τοῦ καταιβάτου Διὸς βωμὸς ὃν καὶ Μόριον καλοῦσιν τῶν ἐκεῖ μοριῶν παρὰ τὸ τῆς Ἀθηνᾶς ἱερὸν ἱδρυμένων. That Zeus Kataibates should have been called Μόριος (μορία) points to some relation with Athena and the olive which may have had its origin on the Acropolis. Does this double name simply mean that Zeus "of sleepless eye" used lightning (καταιβάτης) to avenge sacrilege which one committed when he violated a sacred olive (μορία) as Miss Harrison, Mythology and Monuments of Ancient Athens, p. 599, suggests, or is the key to the explanation furnished by a passage in Pausanias (IX, 12, 4)? Pausanias records the tradition that at the time Zeus hurled the thunderbolt which destroyed Semele and her bridal chamber a log fell from heaven which Polydorus adorned with bronze and called Dionysus Cadmus. Perhaps the ancient image of Athena, the xoanon of olive wood, which fell from heaven, fell at the time Zeus smote Erechtheus, just as the wooden image of Dionysus Cadmus fell when Zeus destroyed Semele. If so, then Zeus Kataibates, by bringing to earth a piece of sacred olive (μορία) very naturally acquired the name Zeus Morios.
What known altar to Zeus in the vicinity of the Erechtheum could have been erected to him in his capacity as καταιβάτης? There was an altar of Zeus Herkeios under the olive in the Pandroseum. This, however, cannot have served as an altar of Zeus Kataibates because these were two distinct phases of the Zeus cult. Pausanias found near the ruins of the palace of Oenomaus at Olympia an altar to Zeus Herkeios and another to Zeus Keraunos (Kataibates). Before the entrance to the Erechtheum Pausanias found an altar to Zeus Hypatus beside the sacred indentations in the rock which lay beneath an opening in the roof, and this is none other than the altar to Zeus Kataibates.
The passage which led from these indentations through the foundation into the temple was not intended for the worshipper but for the priest on occasion. Herein lies a possible explanation of the hole which opens into the passage close to the wall east of the main door. It was perhaps a sort of speaking tube for subterranean utterances. Perhaps beneath the floor of the temple the chthonic Erechtheus was invoked and priestly response heard from above through the opening.
The trident-mark and the well, both destroyed when the mediaeval cistern was cut, were situated in the southwest part of the Erechtheum. Thus evidences produced by Poseidon in the dispute over the land were close to the olive tree of Athena which stood in the Pandroseum. The door in the west wall gave ready access from one to the other.
It has already been remarked that in the description of the Erechtheum, Pausanias gives no indication between the words ἐσελθοῦσιν (I, 26, 5) and συνεχής (I, 27, 2) that he left the building to enter a temple of Athena. The reference to the well and the trident-mark is followed by a compound sentence, the first member (μέν) of which prepares the way for the more important second member (δέ) which tells of the ἁγιώτατον ... Ἀθηνᾶς ἄγαλμα. There is no break here in the continuity of the account and no disturbance of an orderly advance if Pausanias found a means of communication between the inner chamber of the διπλοῦν οἴκημα and the ναὸς τῆς Ἀθηνᾶς. Now the traditional intimacy of Athena and Erechtheus would lead one to expect such communication and thus the cella of Athena which gave the official name to the temple would have a share in the magnificent north portal, the main entrance to the building. The attempts to raise the eastern portico to the dignity of the πρόστασις ἡ πρὸς τοῦ θυρώματος are unsatisfactory. Thus Penrose (op. cit., p. 95): "It may seem a difficulty to explain why the most magnificent portico should lead to a subordinate shrine, but the eastern portico with its six columns, although of smaller diameter, was scarcely if at all of less importance, and the doorway could not have been much inferior in width and height.... The difference of level also obviously gives preëminence to the eastern site." These considerations neither qualify the difficulty nor do they lessen the preëminent magnificence of the north porch. Apart from the demands of the text of Pausanias, there is another point to be observed. From the north porch there was a doorway opening into the Pandroseum. Thus the north porch gave admission to a temenos, but not according to present theory to the eastern cella of Athena.
In the inner chamber where Pausanias saw the well, he must have found a door, the second of the two mentioned in the Chandler inscription, which opened into the eastern cella (Fig. 7). When he had seen the objects there, he retraced his steps past the well and the mark of the trident, and entered by the small door in the west wall, the Pandroseum, where stood a temple which was συνεχὴς τῷ ναῷ τῆς Ἀθηνᾶς. That Pausanias on approaching the Erechtheum should call it Ἐρέχθειον and then on leaving should call it ναὸς τῆς Ἀθηνᾶς is not only quite in keeping with that stylistic tendency which Robert has termed oratio variata (Pausanias als Schriftsteller s.v.) but has a simple and natural explanation. The first name for the temple was that of the western part which he entered first and found to be double; the last name was that of the eastern part which he visited last. The name for the whole was determined by that part which was most prominently in his thought at the time. He gives not the slightest hint that Athena had any share in the temple until he has described the contents of the διπλοῦν οἴκημα. Properly speaking the western part of the building was the Erechtheum, and the eastern, the temple of Athena; but the name of either half spread to the whole, a natural tendency which gave the Parthenon its name, and readily intelligible in the case of the Erechtheum in view of the traditional intimacy of the two divinities recorded in Homer. When Pausanias speaks of the tholos at Epidaurus a second time, he does not call it by that name, but οἴκημα περιφερές. As for the dog of Philochorus, one may believe simply that the creature passed through the Erechtheum proper into the Pandroseum (Petersen, op. cit., p. 143).