Update: I've added a timeline and made some layout changes to make it easier to read.

All right, I've been thinking about this for a while now. It's not the epic Star Trek/Stargate crossover fic that I've been meaning to do for half a year, but it's probably my most ambitious fic yet. I'm not a huge Halo fan, though I've finished Halo 1 and am almost finished Halo 2. But I am a big Stargate fan, and I've been disappointed at the lack of crossover fics, especially complete ones.

AU/Crossover; In the future, the Covenant, a religious alliance of several races has declared war on humanity. Among their defenses is the recently-formed SGC, a branch of the military that uses a device called a Stargate, which allows instant travel between planets.

Timeline

~50000000 BCE - Ancients arrive in Milky Way

50000000 BCE-10000000 BCE - The Ancient empire expands across the Milky way. The Stargate network is built.

~10000000 BCE - Flood begin infesting the galaxy and the Halos are built by the Ancients as a backup plan.

~5000000 BCE - In desperation, the last Ancients leave the Milky Way and fire the Halo rings.

~4900000 BCE - Life begins reappearing in the Milky Way. It is believed but not confirmed the Ancients are responsible.

~16000 BCE - Ra becomes the dominant System Lord among the Goa'uld, a race of human-infesting parasites who pose as gods.

14000 BCE - Goa'uld begin expanding into the galaxy.

9000 BCE - Earth is completely enslaved by Ra.

8200 BCE - Dissent begins to grow between two factions of San 'Shyuum ("Prophets") regarding the treatment of Forerunner (Ancient) artifacts.

8100 BCE - San 'Shyuum civil war ends with the destruction of the homeworld. The Reformists escape on the incomplete High Charity- a city-ship.

7980 BCE - Sangheili ("Elites") discovered by the San 'Shyuum. The Sangheili and the Reformists disagree on the treatment of Forerunner artifacts and a war erupts.

7910 BCE - The Sangheili merge to form the Covenant after a long and bloody struggle.

7900 BCE-7300 BCE - Height of the Covenant empire. The Lekgolo ("Hunters") and Unggoy ("Grunts") join the Covenant during this period.

7289 BCE - First contact between the Covenant and the Goa'uld is made. It ends in disaster for both sides.

7200 BCE-6500 BCE - Goa'uld/Covenant war. The Covenant have a technological advantage in some areas, but are lacking in others, most notably hyperdrives. The Goa'uld lose ground for hundreds of years, using the Stargates and superior drive systems to their advantage. However, their empire is largely destroyed by 7000 BCE. Most System Lords are dead by 6500 BCE, the "official" end of the war. However, pockets of Goa'uld would remain for centuries.. Most human worlds are kept enslaved by their new Covenant masters.

3000 BCE - The humans rebel and Ra abandons Earth. Ra takes the Stargate with him

289 CE - Anubis, the last of the Goa'uld, is killed.

2032 - Earth's other Stargate is discovered below Antarctica. Its purpose is unknown at this time.

2080 - Humans settle on Luna, Mars, and the Jovian moons.

2160 - Armed conflict breaks out between various political factions on Earth and her colonies. The Stargate was lost some time during the conflict.

2170 - Fighting officially ends, with a United Earth Government and the UNSC formed as a result. Rebellions would occur sporadically for the next hundred or so years.

2291 - Partially based on Ancient and Goa'uld artifacts left on Earth, the first Earth-built hyperdrive is built and tested. Although the first test resulted in the tragic loss of the prototype ship and her crew, later tests were more successful.

2298 - Earth's first true interstellar spacecraft, the Da Vinci, is built.

2310 - Humanity begins to spread across the galaxy, colonizing nearby planets. At this time, hyperdrives are prohibitively expensive, slow, and prone to exploding.

2310-2525 - Humanity expands rapidly, inhabiting hundreds of worlds by 2500. Technological advancements result in faster and more powerful ships, increased lifespans, and a massive increase in industrial capacity. However, only a tiny portion of the galaxy is explored.

2461-2467 - The Inner Colony War almost results in the destruction of Earth. Though a swift end is put to it, it is only a taste of what is to come.

2462 - The Unggoy Rebellion occurs. An Arbiter is sent in to quell it, doing so successfully. This marks the beginning of the Age of Doubt on the Covenant calendar.

2490 - Insurrectionist forces begin rising up. The conflict between the UNSC and Insurrectionists will go on until first contact with the Covenant.

2491-2506 - ORION/Spartan 1 program is reactivated. Though successful, it was abandoned in 2506, with key personnel reassigned.

2517 - SPARTAN-II program begins, with 75 specially selected children removed from various worlds. Just under 40 make it through augmentation and training.

2525 - First contact is made with the Covenant on Harvest. Misinterpreting a religious message, they glass the entire planet. This even marks the beginning of the Age of Reclaimation. The Insurrection ends as humanity is united against the Covenant. Human-Covenant war begins.

2541 - Stargate is rediscovered and SGC is formed. Though initially regarded as little more than a top-secret joke, it was successful at retrieving valuable technology and carrying out special operations deep behind enemy lines.

2552 - Current Year. The UNSC fortress world of Reach is destroyed by the Covenant and the Halo rings are discovered.

"Over the last several years, we've made several technological advances thanks to the SGC," Dr. Rodney McKay bragged to the assembly of officers and representatives from military-industrial contractors. The presentation on the history of the SGC had taken longer than he thought it would, and he was anxious to pass these people onto Sam and Daniel. They were probably wondering why he took so long already. "We've also had several military victories, though that's not really in my purview."

"Such as?" asked an army officer.

"Well, um, that's not really part of my job," McKay dodged, "Anyway, we've made many technological advancements, both of military and civilian uses. One of the most useful is the naquadah generator. It's based on a super-heavy element and can produce power far more efficiently than fusion or boosted fusion."

"Dr. McKay, if I read the mission reports correctly, we didn't invent that." stated Admiral James Pickett.

"Well, that is true, sort of. We were assisted by refugees from a world destroyed by the Covenant. But we were able to increase efficiency significantly.

"We've also developed better weapons, armor and shields. I guess I'll uh, turn you over to Major Carter and Dr. Jackson now. Thank you." Dr. McKay led the procession out and than disappeared.

Admiral Pickett almost got the two mixed up. Had they not been wearing nametags, he would have guessed the male one was Carter and the female one was Jackson. Both had similar, yet different, pasts. "What do you do here, Dr. Jackson? I thought you were a linguist and archaeologist."

"Well, yes, I am. We tend to run into a lot of old artifacts here."

"Care to explain, Doctor?" asked one of the representatives.

"Okay, but it might take a while. As you know, a long-extinct race used to occupy the galaxy. The Covenant call them the Forerunners and revere them. Here we simply call them the Ancients. They created the Halo rings, as well as the Stargates. Sometimes we find things that they left behind. Most of them are useless trinkets. But some are valuable, even to the military. We don't know what wiped out the Ancients. It wasn't the Flood or Covenant."

"There was also a newer empire that spanned the galaxy. Well, maybe more of a coalition of so-called 'System Lords'. They called themselves the Goa'uld. Anyway, they took humans as slaves and spread them around the galaxy. The Goa'uld were completely destroyed by the Covenant after centuries, maybe even millenia, of war.

"The effect on us? Well, we keep finding humans in the far reaches of the galaxy. Some are primitive or medieval. Some are industrial, and most are used as slaves by the Covenant."

Carter took over at this point, "When we can, we try to free the humans. We try to launch backdoor attacks against the Covenant through the gate. Sometimes it works, sometimes it doesn't. However, I'd say the SGC is safer than frontline combat."

"Dr. Jackson, I've read your file. You never finished the SPARTAN training, why was that?" Pickett stated. He already knew the answer.

"Well, I was rejected. Had the wrong psychological profile, they said. Apparently that's the only thing they forgot to consider. I wasn't the only one they had to reject."

"Can we move on, please? Thank you." interjected Carter, "Based on reverse-engineered alien technology, the SGC has developed several types of military equipment. Some of these have begun to enter frontline service. The SGC itself uses in-house developed armor, featuring energy-based shielding, advanced tactical communications, and materials that would have taken years to develop otherwise. From Covenant and other technology we have developed several new weapons better able to take on the Covenant threat."

"Like what?" asked Pickett, demeaningly.

The Major reacted slightly, just enough to be noticable. "Well, the M-699 directed energy weapon is beginning to enter service. It is capable of penetrating most Covenant shielding in a single shot. However, it is not without disadvantages. The M-699 is somewhat bulky and heavy.

"We're going to have to skip the weapons demonstrations, and I apologize for that. However, we are running out of time." She pushed a button on the wall intercom. "Daedalus, beam us up." In a flash of light, the party disappeared.

And reappeared on the bridge of the Daedalus. Rodney McKay and Colonel Steven Caldwell were there, as were various crewpersons.

"The Daedalus is without a doubt the most advanced ship in the UNSC inventory," said Rodney McKay, almost bragging.

"And the most expensive," stated Pickett, "For the price of this ship, we could have had a real cruiser. The Daedalus is barely a frigate."

"Let me assure you, the Daedalus is no ordinary frigate," responded McKay. "It has shields that can withstand weapons fire that would destroy any other ship. The beaming system was reverse-engineered from technology from an extinct race and you can probably imagine how useful that is. The Daedalus is also the fastest ship in the fleet. The naquadah based power core is several times more powerful for a given size than a standard boosted-fusion unit and can sustain higher power levels longer."

"What about weapons?" one of the group asked, genuinely curious.

Carter answered this question. "There are no MAC guns on this ship. Well, not big ones anyway. We've scaled down the technology into small turrets, mostly for point-defence. In addition to anti-fighter missiles, the Daedalus can carry the new Hades missiles. They are the latest and greatest in missile weaponry. Each missile has a small hyperdrive for crossing long distances quickly as well as penetrating shields. Even if a missile fails to penetrate, the adjustable-yield naquadah warhead will probably smash through it anyway."

"I've heard they tried to make this ship a carrier too. Did you SGC people really try to do something that insane?" asked the Admiral, somewhat menacingly.

"Those rumours aren't completely unfounded." It was Caldwell this time. "By no means is the Daedalus a carrier, but it does carry eight Dagger light fighters, two Longsword strike/interceptor craft, and two Pelicans, as well as provisions for land vehicles and a Stargate."

"And what about the Prometheus fiasco? If I remember correctly, it had to be towed back to Earth after the reactor exploded. Sometimes I think the only reason this program still exists is because of Major Carter's father," Pickett accused. Carter flushed slightly, trying very hard to keep her rage under control. One nice thing about being a SPARTAN is being able to kill almost anyone unarmed, but even thinking about doing that to a superior officer would get her court-martialed.

"The reason SGC is still around, Admiral, is because it's produced more results that the Navy," retorted Major General Jack O'Neill, head of the SGC, as he entered the bridge. Which wasn't strictly true, but it was a good comeback.

"General, I respectfully disagree. The navy has kept the Covenant away from Earth and won pivotal battles. The SGC has accomplished nothing of that magnitude. You've only been a thorn in the Covenant's side."

General O'Neill wasn't in the mood to argue. "Admiral, I respectfully request that you shove it. Colonel Caldwell, beam this man back down."

"But-"

"Yes sir."

Carter almost smiled. The General always did have a way with words.

Unlike previous fics of mine, I've actually planned out this story to some degree. So hopefully, it shouldn't go off in some random direction or have a rushed conclusion. New chapters should come fairly quickly. As always, please leave a review.