Acts which caused damage to another opened a new class of cases. The law obliged the wrong-doer to make reparation, and this responsibility extended to damages arising not only from positive acts, but from negligence or imprudence. In cases of libel or slander, the truth of the allegation might be pleaded in justification. In all cases it was necessary to show that an injury had been committed maliciously; but if damage arose in the exercise of a right, as killing a slave in self-defence, no claim for reparation could be maintained. If any one exercised a profession or trade for which he was not qualified, he was liable to all the damage his want of skill or knowledge might occasion,--a provision that some of our modern laws might advantageously revive. When any damage was done by a slave or an animal, the owner of the same was liable for the loss, though the mischief was done without his knowledge and against his will. If anything was thrown from a window giving on the public thoroughfare so as to injure any one by the fall, the occupier was bound to repair the damage, though done by a stranger. Legal claims might be transferred to a third person by sale, exchange, or donation; but to prevent speculators from purchasing debts at low prices, it was ordered that the assignee should not be entitled to exact from the debtor more than he himself had paid to acquire the debt, with interest,--a wise and just regulation. By the ancient constitution, the king had the prerogative of determining civil causes. The right then devolved on the consuls, afterward on the praetor, and in certain cases on the curule and plebeian ediles, who were charged with the internal police of the city. The praetor, a magistrate next in dignity to the consuls, acted as supreme judge of the civil courts, assisted by a council of jurisconsults to determine questions in law. At first one praetor was sufficient, but as the limits of the city and empire extended, he was joined by a colleague. After the conquest of Sicily, Sardinia, and the two Spains, new praetors were appointed to administer justice in the provinces. The praetor held his court in the comitium, wore a robe bordered with purple, sat in a curule chair, and was attended by lictors.