Simplify the following text for a Grade 8 native English-speaking person.
Original: The Gauls destroyed all of Rome 's historical records when they sacked the city after the Battle of the Allia in 390 BC ( Varronian , according to Polybius the battle occurred in 387\/6 ) , so no contemporary records of the kingdom exist , and all accounts of the kings must be carefully questioned .
Simplified: The Gauls destroyed all of Rome 's historical records when they sacked the city after the Battle of the Allia in 390 BC or 387\/6 , so no contemporary records of the kingdom exist . All accounts of the kings must be questioned .