They hid contemporary Roman reporting of Jesus Christ. One of the most famous Roman historians Tacticus said:

Therefore, to stop the rumor, Nero substituted as culprits and punished in the utmost refinements of cruelty, a class of men, loathed for their vices, whom the crowd styled Christians. Christus, the founder of the name, had undergone the death penalty in the reign of Tiberius, by sentence of the procurator Pontius Pilatus, and the pernicious superstition was checked for a moment, only to break out once more, not merely in Judea, the home of the disease, but in the capital itself, where all things horrible or shameful in the world collect and find a vogue.1

So they had Roman contemporary historical accounts of Jesus that they said were late Christian additions, and forgery and anachronistic. But now they’re looking more valid and the possibility of foul play has been mostly abandoned. Why were they so motivated to discredit Roman accounts of this pernicious rebellious religion in the Roman territory? Because Jesus is real, and even non Christian romans knew he was real and doing some of impressive things.