In answer to your question about when the game takes place:
@dusk_bot, on May 14 2006, 05:34 PM, said in Cythera Timeline:
...It seems that the game takes place in around the year 918, as Hadrian tells you that his mother passed away "recently" and she died in 917.
005: Odemia is settled as a hunting village "5 years after our arrival from Thera". -Mage Anisa
113: Catamarca "founded in 113 as a retreat for the first Tyrant". -Mage Anisa, Spas of Catamarca
152: The First Tyrant “exiled the Mages in 152.” from Cademia. -Mage Anisa, History of Kythera
153: Pnyx "...founded in 153 by the exiled Mages...” -Mage Anisa
158: Chrysothemus born (Alaric’s mother). -Gravestone in Catamarca
174: “174 when the Second Tyrant built the Citadel.” -Spas of Catamarca
180: Cipher Manuscript discovered in "...the bottom of a chest in the library oh Pnyx." -Histroy of the Cipher Manuscript
184: Abydos founded “In 184... down the coast from Pnyx.” -Mage Anisa
192: Abydos destroyed "...when all communication from there was cut off. When an expedition was sent, they discovered everybody gone from the settlement, but no sign of violence.” -Mage Anisa
201: Chrysothemus dies (Alaric’s mother). -Gravestone in Catamarca
203: Diones the Elder personally begins investigations into the "Cult of Scylla" -Report on Hidden Chiefs and the Cult of Scylla
216: Alaric “...appeared in 216. He ended their rule.” -Mage Anisa
219: The "...current system of government was established" and the "...return of us Mages.” -Mage Anisa
303: Kosha is founded by “...House Comana in 303.” -Mage Anisa
663: First golem "...created...by a mage whose name is obscured in history." -Mage Anisa
700: Golems are "...still being created" despite known problems. -Mage Anisa
720: Golems "...had been outlawed," and "...an attempt to destroy existing 'wild' golems was begun." Mage Anisa
742: Unknown event. -Rings through-out Cythera bearing the inscription “742 - Will to Union”. Semius the golem hunter "...disappeared here in Cademia..." -Mage Anisa
870: Lyons born (Hadrian’s father). -Gravestone in Catamarca
873: Andra born (Hadrian’s mother). -Gravestone in Catamarca
878: Hapmondis born (unknown). -Gravestone in Catamarca
882: Andromache born (unknown). -Gravestone in Catamarca
910: Lyons dies (Hadrian’s father). -Gravestone in Catamarca
917: Andra dies (Hadrian’s mother). -Gravestone in Catamarca
918: Andromache dies (unknown). Hapmondis (unknown) dies. -Gravestones in Catamarca
I think the 600 years of silence (or about that) is because during that time Alaric ruled benevolently and effectively; there is little to talk about with no uprisings or cults etc.
As for the date on the Webboard-Cythera... not more than 50 years after the game, is my guess, as many of the characters (such as Hadrian, Lindus) are still alive.