D is for Duir
The seventh tree is the oak, the tree of Zeus, Jupiter, Hercules, the Dagda (the chief of the elder Irish gods), Thor, and all the other Thunder-gods, Jehovah in so far as he was "El," and Allah. The royalty of the oak-tree needs no enlarging upon: most people are familiar with the argument of Sir James Frazier's Golden Bough, which concerns the human sacrifice of the oak-king of Nemi on Midsummer Day. The fuel of the midsummer fires is always oak, the fire of Vesta at Rome was fed with oak, and the need-fire is always kindled in an oak log. When Gwion writes in the Cad Goddeu, "Stout Guardian of the door, His name on every tongue," he is saying that doors are customarily made of oak as the strongest and toughest wood and that "Duir," the Beth-Luis-Nion name for "oak" means "door" in many European languages including Old Goidelic dorus, Latin foris, Greek thura, and German tur, all derived from the Sanskrit Dwr, and that Daleth, the Hebrew letter D means "door" - the "l" being originally an "r." Midsummer is the flowering season of the oak, which is the tree of endurance and triumph, and like the ash is said to "court the lightning flash." Its roots are believed to extend as deep underground as its branches rise in the air - Virgil mentions this - which makes it emblematic of a god whose law runs both in heaven and in the Underworld. Poseidon the ash-god and Zeus the oak-god were both once armed with thunderbolts; but when the Achaeans humbled the Aeolions, Poseidon's bolt was converted into a trident or fish-spear and Zeus reserved the sole right to wield the bolt. It has been suggested that oak oracles were introduced into Greece by the Achaeans: that the originally consulted the beech, as the Franks did, but finding no beeches in Greece transferred their allegiance to the oak with edible acorns, its nearest equivalent, to which they gave the name phegos - which, as has been mentioned, is the same word as fagus, the Latin for beech. At any rate the oracular oak at Dodana was a phegos, not a drus, and the oracular ship Argo was, according to Appolonius Rhodius, largely made of this timber. But it is more likely that the Dodona oracle was in existence centuries before the Achaeans came and that Herodotus was right in stating on the authority of the Egyptian priests that the black dove and oracular oak cults of Zeus at Ammon in the Libyan desert and of Zeus at Dodona were coeval. Professor Flinders Petrie postulates a sacred league between Libya and the Greek mainland well back into the third millennium B.C. The Ammon oak was in the care of the tribe of Garamantes: the Greeks knew of their ancestor Garamas as "the first of men." The Zeus of Ammon was a sort of Hercules with a ram's head akin to a ram-headed Osirus, and to Amen-Ra the ram-headed sun god of Egyptian Thebes from where Herodotus says that the black doves flew to Ammon and Dodona.
The month, which takes its name from Jupiter the oak-god, begins on June 10th and ends on July 7th. Midway comes St. John's Day, June 24th, the day on which the oak-king was sacrificially burned alive. The Celtic year was divided into two-halves with the second half beginning in July, apparently after a seven-day wake, or funeral feast, in the oak-king's honor.