Titus Livius (Livy), The History of Rome, Book 1
Rev. Canon Roberts, Ed.

36. He¹ was also making preparations for surrounding the City with a stone wall when his designs were interrupted by a war with the Sabines. So sudden was the outbreak that the enemy were crossing the Anio before a Roman army could meet and stop them. [2] There was great alarm in Rome. The first battle was indecisive, and there was great slaughter on both sides. The enemies' return to their camp allowed time for the Romans to make preparations for a fresh campaign. Tarquin thought his army was weakest in cavalry and decided to double the centuries, which Romulus had formed, of the Ramnes, Titienses, and Luceres, and to distinguish them by his own name. [3] Now as Romulus had acted under the sanction of the auspices, Attus Navius, a celebrated augur at that time, insisted that no change could be made, nothing new introduced, unless the birds gave a favourable omen. [4] The king's anger was roused, and in mockery of the augur's skill he is reported to have said, ‘Come, you diviner, find out by your augury whether what I am now contemplating can be done.’ Attus, after consulting the omens, declared that it could. ‘Well,’ the king replied, ‘I had it in my mind that you should cut a whetstone with a razor. Take these, and perform the feat which your birds portend can be done.’ It is said that without the slightest hesitation he cut it through. [5] There used to be a statue of Attus, representing him with his head covered, in the Comitium, on the steps to the left of the senate-house, where the incident occurred. The whet-stone also, it is recorded, was placed there to be a memorial of the marvel for future generations. [6] At all events, auguries and the college of augurs were held in such honour that nothing was undertaken in peace or war without their sanction; the assembly of the curies, the assembly of the centuries, matters of the highest importance, were suspended or broken up if the omen of the birds was unfavourable. [7] Even on that occasion Tarquin was deterred from making changes in the names or numbers of the centuries of knights; he merely doubled the number of men in each, so that the three centuries contained eighteen hundred men. [8] Those who were added to the centuries bore the same designation, only they were called the ‘Second’ knights, and the centuries being thus doubled are now called the ‘Six Centuries.’