In all cases brought before the courts, the burden of proof was with the party asserting an affirmative fact. Proof by writing was generally considered most certain, but proof by witnesses was also admitted. Pupils, lunatics, infamous persons, interested parties, near relatives, and slaves could not bear evidence, nor any person who had a strong enmity against either party. The witnesses were required to give their testimony on oath. In most cases two witnesses were enough to prove a fact. When witnesses gave conflicting testimony, the judge regarded those who were most worthy of credit rather than those who were most numerous. In the English courts the custom used to be as with the Romans, of refusing testimony from those who were interested; but this has been removed. On the failure of regular proof, the Roman law allowed a party to refer the facts in a civil action to the oath of his adversary. Under the Roman republic there was no appeal in civil suits, but under the emperors a regular system was established. Under Augustus there was an appeal from all the magistrates to the prefect of the city, and from him to the praetorian prefect or even to the Emperor. In the provinces there was an appeal from the municipal magistrates to the governors, and from them to the Emperor, as Paul appealed from Festus to Caesar. Under Justinian no appeal was allowed from a suit which did not involve at least twenty pounds in gold. In regard to criminal courts among the Romans during the republic, the only body which had absolute power of life and death was the _comitia centuriata_. The senate had no jurisdiction in criminal cases, so far as Roman citizens were concerned. It was only in extraordinary emergencies that the senate, with the consuls, assumed the responsibility of inflicting summary punishment. Under the emperors, the senate was armed with the power of criminal jurisdiction; and as the senate was the tool of the imperator, he could crush whomsoever he pleased.