Tacitus

The Tacitus was a spherical object with strange symbols covering its whole surface. It contained a vast amount of alien information, "Millions of teraquads of data," to quote Dr. Boudreau. It was unique as a data source in that it was difficult to read the Tacitus while it was incomplete, while it was easy to read once it was complete, similarly to how a computer program malfunctions when missing an important file.

Kane found the Tacitus first, having acquired it from an alien ship. He realized that it was critically important, and while he could translate it himself, he enlisted the services of the mutant leader Tratos to help him with the translation. Other than Tratos, Cabal was the only entity other than Kane that knew how to translate the Tacitus. Kane used this technology to produce several important pieces of technology, such as the Banshee aircraft. More importantly, the Tacitus also allowed him to create a world altering Tiberium missile. However, before he could use the missile, his temple was overrun by GDI forces, who discovered the Tacitus in the wreckage of Kane's Temple of Nod.

The second technology Kane developed was the liquid tiberium technology, which in addition to developing an arsenal of new weaponry, allowed him to lure the Scrin to earth to acquire their teleportation Gateways, to begin a new chapter in humanity's history.

After GDI found it, they had great difficulty translating it. However, they realized that it was the source behind the Tiberium missile, and possibly several other weapons. At this time, the beginning of the Firestorm Crisis, it was their only lead towards preventing the rise in atmospheric contamination caused by Tiberium. To this end, they attempted to have it transferred from the Cairo Temple to a GDI research center and delivered to Tratos for decryption.

Before that happened, however, Cabal had Tratos assassinated, and GDI was forced to 'capture' Cabal, and have him translate it. However, Cabal informed them that a second piece of the Tacitus was needed to complete the translation. Once GDI recovered the second piece, Cabal turned on his former masters, intent on using the Tacitus for himself. By the time that the resulting Firestorm Crisis had been dealt with, Cabal had used the Tacitus to create a second doomsday weapon, the incredibly powerful Core Defender. Fortunately, GDI was able to recover the Tacitus after having destroyed both CABAL's core and the Core Defender

It was discovered by GDI that, with the addition of the second piece of the Tacitus, no decryption or translation was necessary. With this data, GDI was able to use it's sonic emitter technology to break down Tiberium, decontaminating red zones into yellow zones and eventually the blue zones. The emitters also decontaminated the oceans of Tiberium alage. Ironically, the sonic technology needs Tiberium to work.

The mere existence of the Tacitus remains Top Secret. Only the highest echelons of GDI and Nod military command know what it is, and the information it contains.

The Warning
It was also revealed that both Kane and GDI had gleaned information about the arrival of an advanced alien species to Earth, in the case of a Liquid Tiberium explosion. GDI saw this as a warning, while Kane viewed it as instructions on how to "invite" a race of beings with great knowledge of Tiberium to Earth. Despite considering the Scrin as "visitors" Kane did take the liberty to prepare specially designed missiles for use against them. The GDI modifications to the Ion Cannons, allowing them to engage non-terrestrial, high speed targets may also be because of this.

The intelligence about the Scrin apparently is incomplete, even though GDI has spent years studying the Tacitus. However, it is clear that whatever desgined the Tacitus was different from the invaders, but referred to them as; "brother", "ascended", "enemy", and finally "Scrin". Although it seems unlikely the Tacitus was a direct product of the Scrin, it is fairly obvious that the makers were completely aware of them.

Naming
Kane named the alien data matrix after Publius Cornelius Tacitus, a well known Roman historian known for his works the Annals and Histories. This is similar to Kane's claim to have named Tiberium after the Roman Emperor Tiberius.