The Mouvelian Calendar

The Mouvelian calendar (named after Grand Patriarch Mouvel, the first high priest of the Church of Dwayna) begins counting years from the moment the gods left Tyria. This event is known as the Exodus. Years before this date are labeled BE (Before the Exodus). Years after this date are AE (After the Exodus). Years prior to the year 1 AE count down, getting smaller as they get closer to the time of the Exodus (just as they do in the Gregorian calendar).

There are four seasons and 360 days in the Mouvelian year:
Season of the Zephyr (Air aligned) days 1-90
Season of the Phoenix (Flame aligned) days 91-180
Season of the Scion (Water aligned) days 181-270
Season of the Colossus (Earth aligned) days 271-360

Calendar starts at year 1 AE (The first year after the Exodus)

1072 AE Present Day
1071 AE Bay of Sirens is renamed Sea of Sorrows
1070 AE Guild Wars end
1070 AE Charr invade human kingdoms
1013 AE Guild Wars begin
898 AE Great Northern Wall is erected
851 AE Lord Odran enters the Rift
358 AE Kryta becomes an independent nation
300 AE Kryta becomes a colony
221 AE Cantha begins trading with Tyria
174 AE Serpents leave the world of men
2 AE Orr becomes an independent nation
1 BE Gods give magic to the races of Tyria
100 BE High-plains human settlements become known as Ascalon
205 BE Humans appear on Tyrian continent
1,769 BE Serpents arrive in Tyria
10,000 BE Last sign of Giganticus Lupicus (the giants) walking on Tyrian continent (best guess)
http://eu.guildwars.com/gameplay/theworld/timeline/