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Timelines of the Battlestar Galactica series
By convention, all dates are relative to the Fall of the Twelve Colonies. Events before the Fall are marked as "BCH", or "Before Cylon holocaust". Given the few and somewhat contradictory dates about the Colonials' ancient history and the exodus from Kobol, that part of the timeline is speculative.
The Cylon holocaust occurs more than 150,000 years ago.
- Unspecified time period: Humans on the planet Kobol organize themselves into twelve tribes (TRS: "Miniseries"). According to at least one scripture, they "live in utopia with the gods." The humans become sufficiently advanced to establish viable space travel and artificial, robotic life. Artificial life-forms, machines similar in nature to the later day Cylons, are created by the humans. A war against the machines occurs. At one point the machines evolve and take humanoid form, either before, during or after the war. This group of humanoid Cylons are later referred to in the Sacred Scrolls as the "Thirteenth Tribe," although said text does not specify that they were a tribe of Cylons (Sometimes a Great Notion).
- Over 17,000 years BCH: A supernova creates the Ionian nebula.
- ca. 4,000 years BCH: The Thirteenth Tribe reportedly leaves Kobol and builds the Temple of Hopes on another planet  This contradicts Ellen Tigh's statement that the temple was built 3,000 years ago (No Exit). They pray for guidance and are shown the way to Earth, the planet they colonize.
- ca. 3,600 years BCH: Pythia records her prophecies. Aside from reports of the landing on Earth and drawings of temples there, this book describes "the exile and rebirth of the human race" and a "dying leader" not making it to a "promised land," though how long before her writings that such events took place is not revealed.
- ca. 3,000 years BCH: A beacon is left at the Lion's Head Nebula, later marking the way to Earth. At some undated point, someone travels from Earth to Kobol, passing on information about Earth, including a map of its night sky 
- ca. 3,000 years to 2,000 years BCH: The humanoid Cylons of the Thirteenth Tribe prosper and begin to reproduce sexually. The technology of "organic memory transfer," or downloading, is abandoned.
- The Thirteenth Tribe produce their own mechanical Centurions to act as laborers for their civilization.
- ca. 2,000 years BCH: (The order of events on Kobol and Earth is uncertain.)
- Samuel Anders, Tory Foster, Ellen Tigh, Saul Tigh, and Galen Tyrol, later collectively known as the "Final Five," are born on Earth.
- The Final Five work together in a research lab attempting to re-develop downloading technology. The effort is spearheaded by Galen Tyrol and Ellen Tigh.
- All five Cylons receive visions of beings nobody else can see warning them of an impending rebellion by Earth's Centurion population. The Final Five prepare a resurrection ship and leave it in orbit.
- The remaining Twelve Tribes leave Kobol and settle the Twelve Colonies.
- Lord of Kobol "Athena" kills herself in despair over this. A tomb is built for her containing a 3-D projection showing Earth and its Zodiac. The projection is activated by the Arrow of Apollo, which travels with the twelve tribes.
- The Centurion uprising occurs and the Thirteenth Tribe exterminates itself in a nuclear holocaust. Earth is left a nuclear wasteland. The Final Five die in the attack, and are resurrected on board their orbiting ship.
- The Final Five begin a journey back to Kobol to find the other twelve tribes and inform them of Earth's fate. They are aware of the cyclical nature of history and believe that the twelve tribes will create Cylons again. They want to warn them to treat them right. However, their ship is not equipped with a conventional FTL drive and journeys at relativistic sublight speeds.
- 2,000 years to 52 years BCH: The Twelve Colonies grow and prosper. Each colony acts as a sovereign nation, complete with inter-colonial wars.
- The Final Five stop at the Temple of Hopes as they retrace their tribe's path.
- The Final Five arrive at Kobol, finding the planet abandoned. They continue on in pursuit of the twelve tribes, heading toward the colonies.
Recent Colonial History
The most recent history could also be dated using the calendar from Caprica, but the method was not used in the re-imagined series and remained in the background even on the new show. Furthermore, it is not known whether the calendar is specific to the planet Caprica or common to the twelve worlds.
- At least 200 years BCH: Humans develop an immunity to the virus causing Lymphocytic encephalitis (A Measure of Salvation). 
- ca. 93 BCH: Tauron Civil War causes emigration of Joseph and Sam Adama to Caprica to live in an orphanage. Joseph later becomes a lawyer thanks to the education funded by the Ha'la'tha crime syndicate; Sam becomes an assassin for Ha'la'tha (Caprica pilot).
- 69 years BCH:
First Cylon War
- 58—52 years BCH: With the use of a meta-cognitive processor stolen from Tauron rival Tomas Vergis, the Caprican tech CEO Daniel Graystone creates the first Cylons of the Twelve Colonies to aid in hard labor and warfare. A virtual copy of his dead monotheist daughter Zoe Graystone's consciousness is downloaded into one (Caprica pilot). Humanity is unaware that they are repeating the actions of their ancestors on Kobol.
- ca. 58 BCH:
- 52 years BCH:
- 51 years BCH: Colonial ship Brenik is lost after a boarding action by Cylon Centurions (Valley of Darkness, deleted scene).
- ca. 50 years BCH: Battlestar Galactica enters service.
- 42 years BCH:
- William Adama begins his service in the Colonial Fleet as a Raptor pilot aboard Galactica with co-pilot and ECO Coker Fasjovik, 10 years into the Cylon War ("Hero", Blood and Chrome). He is later promoted to Lieutenant and is assigned his first Viper, a Mark III, and a special task force comprised of top pilots for dangerous missions.
- Battlestar Archeron destroyed by Cylon forces in Sector 12. All hands lost (TRS: "Blood and Chrome").
- Battlestar Osiris destroyed over Djerba in suicide maneuver against lone Cylon Baseship. All hands lost. Fate of Lt. Jim Kirby (AWOL) unknown.
- Becca Kelly succeeds in her mission on Djerba, and is later killed by the Cylons. Ghost Fleet Offensive successful, decimating Cylon military holdings in five sectors.
- Mechanical Cylons begin experiments constructing humanoid forms of Cylon.
- 42-41 years BCH: Coker Fasjovik presumably musters out of Fleet after termination of second mandatory tour.
- 40 years BCH:
- Experiments on "humanoid" Cylons culminate in the creation of the First Hybrid and subsequent Hybrids, but no fully humanoid forms.
- The Final Five arrive in the Twelve Colonies in the waning days of the war.
- The Five meet the local Cylons and negotiate an end to the war. They will give the Cylons biological bodies complete with resurrection technology if the Cylons agree to end the war.
- Operation Raptor Talon conducted by the Colonial Fleet, where William Adama flies his first official Viper mission. Battlestar Columbia destroyed (Razor Flashbacks).
- Armistice ends the Cylon War. Cylons exile themselves from the Twelve Colonies (TRS: "Miniseries"). The First Hybrid and his Guardians part company with the other Cylons.
- William Adama musters out of the Colonial Fleet ("Scattered", Adama's dossier).
- 37 BCH: William Adama enlists as merchant marine and serves aboard inter-colony freighters ("Scattered", Adama's dossier).
- 37 to ca. 30 BCH:
- The Cylons establish a secret base known as The Colony, built around and connected with the original ship of the Final Five. This is the place where research and development equipment belonging to the Final Five is stored.
- The Final Five create John Cavil, the first of the new humanoid Cylons that are their "children," and designate him model Number One. They raise him for some time.
- John matures and assists the Final Five in the creation of seven other humanoid Cylon models. A resurrection system is built for the new models based on technology left over from the Thirteenth Tribe.
- ca. 30 BCH:
- Cavil murders model Number Seven, Daniel, out of jealousy by poisoning the amniotic fluid in which the Seven copies were maturing.
- The Final Five are murdered by Cavil and their consciousnesses are boxed.
- Cavil erases all knowledge of the Final Five and the missing model Number Seven from his fellow humanoid Cylon models and specifically programs them not to think about either.
- Saul Tigh is resurrected and introduced to the colonies as a military officer with false history of fighting in the war.
- Ellen Tigh is resurrected and introduced into Colonial society sometime thereafter.
- ca. 28 BCH:
- ca. 27 BCH: William and Carolanne Adama meet and marry. 
- ca. 26 BCH: Lee Adama born. 
- ca. 24 BCH: Zak Adama born. 
- 23 years BCH: William Adama reinstated in the Colonial Fleet at the rank of Captain and is assigned to the battlestar Universal  ("Scattered" deleted scene, Adama's dossier).
- 21 years BCH: Saul Tigh reinstated in the Colonial Fleet at the rank of Captain by now-Major Adama (Scattered).  
- 20 years BCH:
- 17 BCH: William Adama assigned to the battlestar Atlantia, where he makes his 1000th Viper landing (Adama's dossier, "Act of Contrition").
- 13 years BCH: William Adama assigned as executive officer to the new battlestar Columbia (Adama's dossier).
- 11 years BCH: Laura Roslin begins her career in politics (Litmus).
- ca. 10 years BCH: Galen Tyrol enlists in the Colonial Fleet as a non-commissioned officer.
- 9 years BCH: William Adama promoted to commander and assigned as commander of the battlestar Valkyrie (Adama's dossier, "Hero").
- 7 years BCH: Saul and Ellen Tigh meet and marry again, unaware that it is the second time ("Kobol's Last Gleaming, Part I", deleted scene).
- 6 years BCH: William Adama leads an aborted covert intelligence mission aboard Valkyrie. Daniel Novacek is shot down and captured by the Cylons. Adama and Tigh are subsequently assigned to Galactica (Adama's dossier, "Hero"). 
- 5 years BCH:
- 4 years BCH:
- 3 years BCH: Felix Gaeta assigned to Galactica (Miniseries).
- 2 years BCH:
- Caprica Six begins residence on Caprica (Downloaded), first encounters Dr. Gaius Baltar (Miniseries).
- Sharon Valerii begins service aboard Galactica (The Farm).
- Zak Adama dies in a flight school accident (Miniseries).
- Lt. Kara Thrace is re-assigned from flight school to Galactica (Act of Contrition).
- 1 Year BCH:
- Between 5 and 1 Year BCH:
- The following events are all seen in "Daybreak, Part I" and "Part II" but are not dated. However, they fall within this approximate time frame.
- Laura Roslin's father and sisters are killed by a drunk driver.
- Kara Thrace and Lee Adama first meet.
- Caprica Six finds Julius Baltar a new home in a retirement centre which encourages horticultural activities.
- William Adama ponders retirement at a security firm but rejects the job in disgust when forced to take a polygraph test.
- Sharon Valerii nearly washes out of the Colonial Fleet, but is given a second chance by Commander Adama. She promises to pay him back for his kindness.
- Laura Roslin joins Richard Adar's presidential campaign.
- Gaius Baltar promises Caprica-Six full access to the Colonial Defence Mainframe if she helps him work on the Command Navigation Program.
Return of the Cylons
- Zero Hour:
- The Cylon fleet gathers at a staging area close to The Colony (The Plan).
- John Cavil makes his final preparations for the impending assault and visits a sealed-off resurrection chamber housing deactivated copies of the Final Five (The Plan).
- The Armistice Station is destroyed by Cylon forces, appear, and show themselves, (albeit in a more advanced form, as well as a humanoid version) for the first time in 40 years.
- Laura Roslin is diagnosed with inoperable breast cancer.
- Galactica is decommissioned.
- A Cavil meets with Caprica Six, who gives him the access codes to the Colonial Defence Mainframe (The Plan).
- The Cylon strike force simultaneously jumps into orbit around all twelve colonies and commences an all-out attack (The Plan).
- The Twelve Colonies are heavily bombarded by nuclear bombs.
- Picon Fleet Headquarters is destroyed.
- Ellen Tigh is placed aboard Raptor from the medical ship Rising Star by John Cavil shortly before it escapes the destruction of Picon ("Tigh Me Up, Tigh Me Down", "No Exit", "The Plan").
- Galactica's last Viper Mark VII squadron is destroyed.
- A battle near Virgon ends with the total loss of the remaining Colonial Fleet including the flagship Atlantia.
- The battlestar Pegasus luckily escapes the destruction of the Scorpion Fleet Shipyards ("Pegasus", "Razor").
- The Cylons begin landing ground forces on the Colonies (The Plan).
- Galactica engages Cylon Raiders and survives with moderate damage and 85 dead.
- Last transmission from the Colonies received by Laura Roslin aboard Colonial Heavy 798 from a fellow secretary.
- Case Orange contingency mechanism assigns Roslin the office of the President of the Twelve Colonies.
- Roslin gathers stranded civilian and military ships in the vicinity of Caprica.
- Commander Adama assumes overall Fleet command and orders regroup at Ragnar Anchorage
- Roslin's fleet survives two Cylon attacks and meets at Ragnar.
- Galactica changes from battle stance to civilian protection, and escorts the civilian fleet from Ragnar towards the Prolmar Sector.
- The Twelve Colonies of Kobol lie in irradiated ruins. Their military has been utterly defeated and their infrastructure has been crushed. The result of the engagement is a complete victory for the Cylon forces (The Plan).
- The Cylon occupation of the Colonies begins (The Plan).
- Tyrol says that "Our initial radiocarbon dating suggests that the temple's at least 4,000 years old, which lines up with the exodus of the Thirteenth Tribe." (The Eye of Jupiter). This is the oldest date noted in the series's timeline, but also conflicts with the prior date of Pythia and her works as described by Elosha in "Kobol's Last Gleaming, Part I", where she states that the exodus of all 13 tribes occurred approximately 2,000 years ago.
- Adama says that "According to Cottle, the virus was an exact match to one reported over 3000 years ago, right around the time that the 13th colony left Kobol" (A Measure of Salvation). This contradicts the two other dates of 2,000 and 4,000 years. While the dating is uncertain, it is the only clue to the beacon's age. That someone traveled back to Kobol is speculation, but an explanation for how Earth's sky could be displayed there. If true, it is still unknown on which of these two voyages the beacon was left behind.
- Doctor Cottle notes the time as "a couple hundred years ago", which is an indeterminate amount of time, but likely less than four or five hundred years.
- From Ronald D. Moore's scifi.com blog post of April 11, 2005: "Colonial Day occurs every year and it is the anniversary of the founding of the "federal" system of government which was a relatively recent event. Before that time, the Colonies functioned more or less on their own, possibly with various attempts at alliances or even complete Colonial government over the centuries since the exodus from Kobol, none of which were successful. When the first Cylons were created, individual Colonies still warred against one another and it wasn't until the Cylon rebellion that the 12 Colonies finally came together in a permanent way. Presumably, the Articles of Colonization were not made up out of whole cloth, however, and there may well be principles and ideas of justice that date back to the original colonists."
- At the time of the Cylon attack, Tyrol has "ten years experience" (TRS: "Miniseries"), and has "served on battlestars since I was 18" (Resistance). This puts his birth in approximately 28 BCH, allowing for a few years leeway with the first comment.
- The podcast for "Scattered" places their meeting "twenty years ago". In "Torn", Adama states that he has known Tigh for 30 years. Furthermore, Adama's dossier places his reinstatement into the Colonial Fleet at 23 BCH. Battlestar Wiki choses to use the more consistent dates.
- This date is assumed as follows: Zak died 2 BCH. Since he graduated from some kind of military academy, he would be at least 22 years old, following real world models. On a photograph of William Adama with his sons, Lee seems to be about two years older than Zak. Adama and his wife probably met not long before Lee's birth.
- This information comes from a prop used in the episode "Scattered".
- The time between Adama's and Tigh's reinstatement is not specified on screen. The February/March issue of Battlestar Galactica: The Official Magazine gives it as two years: "Adama reenlisted with the service and Tigh spent two years drinking before Adama pulled strings to get him back into service."
- In actually, this is Saul Tigh's entrance into the Colonial Fleet, not his return, as he did not serve in the Cylon War and all documents of his service and retirement were forged by John Cavil.
- At the time of the Cylon attack, Tyrol has "ten years experience" (TRS: "Miniseries"). It is likely that Tyrol (and the two other remaining members of the Final Five, Samuel Anders and Tory Foster), was introduced into Colonial society at or around this point by John Cavil as part of his plan for revenge on his creators, human and Cylon alike (No Exit).
- While dialogue from "Hero" places these events at 1 BCH, this contradicts previously established dates about the time Adama and others served on Galactica. See Hero#Analysis for a detailed explanation why Battlestar Wiki chooses to treat this as a continuity error and change the date.
- Since Adama states that Tyrol has been under his commander for "over five years", this might also be one year earlier.