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 relations, and slaves, could not bear evidence, or any person who had a strong enmity against the party. The witnesses were required to give their testimony on oath. Two witnesses were enough to prove a fact, in most instances. When witnesses gave conflicting testimony, the judge regarded those who were worthy of credit rather than numbers. 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. [Sidenote: Condition of debtors.] Under the empire every judgment was reduced to writing and signed by the judge, and then entered upon a register. [Footnote: C. vii. 45, 12.] After the sentence, the debtor was allowed thirty days for the payment of his debt, after which he was assigned over to the creditor and kept in chains for sixty days, during which he was publicly exposed for three market days, and if no one released him by paying the debt, he could be sold as a slave. Justinian extended the period to four months for the payment of a judgment debt, after which, if the debt was not paid, the debtor could be imprisoned, but not, as formerly, in the creditor's house. At first the goods of the debtor were sold in favor of any one who offered to pay the largest dividend, but in process of time, the goods of the debtor were sold in detail, and all creditors were paid a ratable dividend. In no respect are modern codes superior to the Roman, so much as in reference to imprisonment for debt. In the United States it has practically ceased, and in England no one can be imprisoned for a debt under 20 pounds, and in France under 8 pounds. [Sidenote: Appeal.] 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 emperor. In the provinces there was an appeal from the municipal magistrates to the governors, and from them to the emperor. Under Justinian, no appeal was allowed from a suit which did not involve at least twenty pounds in gold. [Sidenote: Criminal courts.]