|“||I have the Tacitus. I am invincible. The Tacitus told me of Tiberium missiles, of invulnerable flying ships, of real-time genetic mutation. More than alien. More than human! The next step in our evolution as a species!
The Tacitus was a data storage device of unknown age and alien origin, brought to Earth by an unknown alien species. The Tacitus contained a massive amount of information, including information about advanced technology, making it highly sought after by both the Global Defense Initiative and the Brotherhood of Nod.
How and when the Tacitus arrived on Earth is unknown. However, at some point in history, presumably in the ancient past, a piece of the Tacitus was broken off of it and placed in the Temple of the Tacitus in Bolivia. Prior to the Second Tiberium War, the Forgotten acquired the Tacitus and studied it in an attempt to find a cure for their Tiberium mutation. However, Tratos, the Forgotten leader, was tricked into translating the Tacitus for Kane. His translation effort was assited by CABAL, an advanced Nod artificial intelligence.
Second Tiberium War
During the Second Tiberium War, Nod developed chemical missiles using knowledge gained from the Tacitus. These missiles were capable of "reformatting" the Earth into pure Tiberium. After Tratos was rescued by GDI forces, he warned them that Kane's ultimate goal was to alter the planet so that it can only support Tiberium-based life, and lamented that by assisting Kane, he had betrayed the world.
After the Forgotten warrior Umagon was captured by Nod forces, Kane brought her to his Pyramid headquarters in Cairo and showed her the World Altering Missile, a Tiberium missile with enough payload to convert the entire planet at once. During GDI's assault on Cairo, Kane boasted to GDI commander Michael McNeil that he was invincible because of the Tacitus, which had given him the knowledge of not just Tiberium missiles, but also "of invulnerable flying ships, of real-time genetic mutation". However, McNeil stabbed Kane with a piece of debris while he was distracted, apparently killing him. He then took the Tacitus and left the collapsing Pyramid with Umagon. 
Restoring the Tacitus
Although the war was won by GDI, Tiberium contamination was reaching critical levels. The Daedalus Team believed the Tacitus to be the best approach to acquiring the necessary knowledge to fight Tiberium. The device and Kane's accumulated notes and data were scheduled to be shipped immediately to the Daedalus Research Complex where Tratos could continue translation. The Tacitus was loaded onto Kodiak at Cairo but the ship was destroyed by an ion storm in flight. This coincided with the beginning of the Firestorm Conflict. As one of its first duties, General Paul Cortez ordered the emergency Firestorm Taskforce to recover the Tacitus. GDI did not locate Kane's store of translated data.
Tratos was assassinated by Nod on CABAL's orders before receiving the Tacitus and translation proceeded slowly. Doctor Gabriella Boudreau estimated Tratos' death put the project years behind schedule, when it was estimated the atmosphere would be toxic to humans within a year. The doctor proposed to use CABAL as a substitute translator; the Nod AI helped Tratos translate the Tacitus for Kane.
The Firestorm Taskforce captured CABAL core in Poland. This was to the AI's design. It knew translation efforts were crippled because the device was physically incomplete. Nod had failed to retrieve the missing segment and it hoped GDI would be more successful. CABAL convinced GDI to retrieve the missing segment after revealing the nature of the problem. The AI even pinpointed the segment's location in northern Bolivia for the Firestorm Taskforce. The segment was sequestered in a complex of ancient step pyramids occupied by a small religious group. A GDI archaeologist deciphered the pyramid hieroglyphs to determine which one the segment was stored in. CABAL took the completed device and unleashed its cyborgs on GDI.
Ironically, the Tacitus was, in turn, stolen from CABAL by the Forgotten. The AI used Nod forces to recover the device for it. The Brotherhood's Inner Circle grew increasingly uneasy with the AI's independence, including its unilateral recovery of the Tacitus and assassination of Tratos. CABAL finally broke with Nod when the Inner Circle threatened to deactivate it.
The Tacitus was retrieved by GDI from a CABAL core at the end of the Firestorm Conflict. While Doctor Boudreau made a series of breakthroughs on the whole GDI continued to struggle with interfacing with the Tacitus and data recovery remained slow.
Signs and Portents
After GDI's recovery of the Tacitus, it was stored in the fortified Cheyenne Mountain Complex for analysis.In the interwar period, further GDI Tacitus research uncovered references to the Scrin and their future invasion. Unbeknownst to GDI the Scrin were a key factor in Kane's strategy for the Third Tiberium War.
Third Tiberium War
Tacitus translation was the responsibility of GDI InOps when the Scrin invaded Earth. They noted the structure of Scrin data transmissions was patterned on the data structure found in the Tacitus, but were significantly different such that it was unlikely the Scrin were the exact originators of the device. Decryption programs similar to those found in the Tacitus were used to interface with and capture Annihilator Tripods.
|“||LEGION, I address you and you alone first. Know that you are more than a mere neural network. Your design is drawn from the Tacitus itself. You are connected to the artifact, now know this. As the Visitors' towers near completion, the Tacitus has begun to transmit a signal. A signal only you can receive. You must find it, liberate it! The Tacitus is the key to Ascension... and beyond!
- Kane to LEGION.
Nod located the Tacitus in China as GDI prepared to transport it away by sea. On Kane's behest, LEGION intercepted and captured the land convoy carrying the device. The AI was maliciously shut down by Abbess Alexa Kovacs before the Tacitus could be extracted. 
The Key to Ascension
|“||They are like children playing with a nuclear weapon! They have no idea what they have, no idea of its power! Their experiments have rendered the Tacitus dangerously unstable, do you see how the signal is fluctuating?! If we are to secure the artifact, we must move quickly, before we lose it forever!
- Kane to LEGION
After LEGION's failed attempt to intercept the Tacitus, it was back under GDI control and was transferred to the Rocky Mountains base. The device's condition was deteriorating and the probability of destroying it increased with every test. Kane was disturbed by the development, and feared GDI may have damaged it beyond repair, but chose to wait until LEGION reactivated in 2052. Nod was much reduced as a result of the Third Tiberium War. The forces needed to assault the Tacitus facility was found in the Marked of Kane. LEGION recovered the Tacitus and interfaced with it.
Kane showed the Tacitus to GDI in 2062. Presumably interfacing with LEGION stabilised the device, since Kane could publicly display it without fear. The advanced knowledge of the Tacitus was later used to create both the Tiberium Control Network and Optical implants.
Command & Conquer 3: Tiberium Wars claimed GDI confiscated the Tacitus from Nod in 2028. However, GDI only confiscated the Tacitus from Nod at the end of the Second Tiberium War, in December 2030. It was then stolen by CABAL and recaptured by GDI at the end of the Firestorm Conflict, which took place even later.
Behind the Scenes
- Westwood Studios originally developed two origins for the device.
|“||We had also developed two completely different origins for the Tacitus, and since both stories leveraged that origin, I'm trying to remember what each included. One was centered around the Tacitus being a soul-prison for the leader of the martian force that fought against the Scrin (they knew how to beat the Scrin, but discovered it too late) while the Earth was still primordial, and the other was centered around the Scrin rebels stealing the "bible" of the Scrin -- which may or may not have been written by them in the first place -- and the Scrin Primal's crusade to recover it.
Both were interesting and had some cool reveals.
- The Tacitus is named after the Roman historian of the same name, who wrote an extensive account of the Roman Emperor Tiberius' reign.