Livy, Ab Urbe Condita 22 8
“Before any certain plans were completed, another disaster was suddenly reported: four thousand cavalry under the command of Gaius Cenentius and sent by the consul Servilius to his colleague in Umbria had turned around after hearing news of the Battle of Lake Trasimene and was trapped by Hannibal.
This news affected people differently: some, whose minds were overcome by a greater sorrow, believed that this recent loss of cavalry was a minor matter when compared to earlier events. Another group did not judge what happened on its own, but just as when a body was already sick any anguish, however minor, would be sensed more deeply than when in wealth, so too this should be judged not by some abstract measure but in realization of the fact that the country was sick and weakened and was incapable of withstanding any more grief.
For this reason, the people took refuge in a solution which had been neither desired nor used for a long time: the declaration of a dictator. But since the consul was away and they believed only he could announce a dictator, and because it was not easy to send a messenger or letter through an Italian countryside overcome by Carthaginian soldiers, the people did something that had never been done before that day: they made Quintus Fabius Maximus dictator and Marcus Mincius Rufus Master of Horse.”
Priusquam satis certa consilia essent, repens alia nuntiatur clades, quattuor milia equitum cum C. Centenio propraetore missa ad collegam ab Servilio consule in Umbria, quo post pugnam ad Trasumennum auditam averterant iter, ab Hannibale circumventa. eius rei fama varie homines adfecit. pars occupatis maiore aegritudine animis levem ex comparatione priorum ducere recentem equitum iacturam; pars non id quod acciderat per se aestimare sed, ut in adfecto corpore quamvis levis causa magis quam in valido gravior sentiretur, ita tum aegrae et adfectae civitati quodcumque adversi inciderit, non rerum magnitudine sed viribus extenuatis, quae nihil quod adgravaret pati possent, aestimandum esse.
Itaque ad remedium iam diu neque desideratum nec adhibitum, dictatorem dicendum, civitas confugit; et quia et consul aberat, a quo uno dici posse videbatur, nec per occupatam armis Punicis Italiam facile erat aut nuntium aut litteras mitti, quod nunquam ante eam diem factum erat, dictatorem populus creavit Q. Fabium Maximum et magistrum equitum M. Minucium Rufum