Much of the Phoenix Gate's history is shrouded in mystery. The details of its creation still lay in the deep recesses of history.
In 975 C.E., the Phoenix gate was in the possession of the Norman princess, Elena, as her dowry. The Archmage wanted possession of the Gate, and sent bandits to attack the approaching Normans to steal the Gate. They were, however, defeated by a time-traveling Xanatos his father, Petros, and David Xanatos' newlywed bride, Fox. The Archmage was enraged, and sent his gargoyle protege, Goliath's mate, to steal the Gate. When she had gotten ahold of the Gate, it sparked in reaction to the approach of a future version of itself. It was Demona, who had come to try to prevent the Wyvern Massacre. Left with terrible knowledge of the future, Goliath's "Angel of the Night" vowed never to become like her future self, and broke the Phoenix Gate in half, giving the other half to her Goliath as a token of their love, telling him to keep it and cherish it always, and she in turn would cherish her half, pledging her heart and soul to him forever.
After the Massacre, Demona fled, always carrying her half with her through the centuries. The other half made its way to Castle Wyvern. Goliath took it to Xanatos' and Fox' wedding, hoping to reunite himself with Demona, but was crushed when Demona revealed she had planned on his sentimental nature; she reunited the two halves of the Phoenix Gate to travel to 975 C.E. to prevent the massacre.
During the travels through time, Goliath, with the help of the younger Demona managed to secure the Gate, promising to himself that none would again use it, for its power was too great.
Months later, Demona and MacBeth stole the Gate, along with the Grimorum Arcanorum, the Eye of Odin, and Coldstone. The Weird Sisters gave the magical artifacts to the present Archmage off the coast of Avalon, who used the Gate to rescue himself from the past, and ultimately to attempt world conquest. Goliath destroyed the Archmage, and he reclaimed the Gate, yet again, and the Eye of Odin, again vowing that none shall use them for their immense power.
He broke that vow to search for the English gargoyle, Griff, whom two previously unknown gargoyles, Leo and Una, claimed that Goliath swore he would protect him in World War II. Goliath used the gate to transport to 1940 C.E., the year Griff disappeared, saving Griff and bringing him forward to 1995.
Puck, in order to escape the approaching Gathering called by Oberon, cast an illusion over Goliath, trying to trick him into handing it over. In order to prevent anyone from getting the Gate, Goliath opened a hole in the time-stream, and threw the Gate into it, losing it forever...or so he thought.
On January 5, 1997 the Phoenix Gate reappeared in front of Brooklyn, Angela, and Broadway. When Brooklyn reached for the Gate, it disintegrated and the Phoenix emerged. It swallowed Brooklyn whole and vanished, leaving Broadway and Angela to wonder if they'd ever see Brooklyn again. Forty seconds later Brooklyn reappeared in the flames, now forty years older, with a mate, Katana, a son, Nashville, and an unhatched egg (Who Brooklyn calls Egwardo)
The Phoenix Gate appears as a small golden shield with a turquoise coloured inset, and a phoenix, also in gold. In order to activate the Phoenix Gate, one must hold it and speak the Latin incantation "Deslegrate muri tempi et intervalia!" (This translates roughly to "Burn down walls of space and time!")
Afterwards, a ball of fire will appear and teleport the speaker and anyone close enough to him or her to whatever time and place the speaker had envisioned. The one known exception was the "enhanced Archmage," who could control the Gate without even a single spoken word, presumably through sheer will.
Time travellers in the Gargoyles Universe, whether using the Phoenix Gate or any other method (no others have yet been discovered), are unable to change history, for the simple reason that they have already been to the past. Thus, Xanatos' trip to 975, the Archmage's trip to 984, and Goliath's trip to 1940, were all events that could not change the past, but merely served as part of it; Xanatos' visit to Castle Wyvern in the 10th century brought about his receiving the rare coin in 1975 that he had already received twenty years before he left, and similarly Goliath's time travel adventure became responsible for the very disappearance of Griff that he had gone to 1940 to investigate. On the other hand, Goliath was unable to return Griff to the Mystic shop during World War II, and both Demona and Goliath failed to alter the pattern of Demona's behavior from 975 onwards, although they both made the attempt. History is immutable; the very attempts to change it become part of the already-existing pattern - were part of it all along.