Ἡ τοῦ διπλοῦ ἀπαίτησις (the actio in duplum) for wrongful damage - A mystery in Byzantine law. In addition to the actio legis Aquiliae utilis and the actio in factum from classical and justinianic law, for cases of indirectly caused damages, Byzantine law also grants an actio in duplum. In this actio in duplum, unlike the two remedies first mentioned, the fine increases to the twofold. Curiously enough, this doubling does not depend on whether or not the defendant denies the damage. In the Basilica we can find for cases of damage to property, when direct causation is lacking, two different remedies for claiming the double, the actio legis Aquiliae with litiscrescence and the actio in duplum. These remedies originate more or less from two different periods. The first remedy we mainly find in jurists from the sixth century. It was only applied in cases of direct caused damages, in which the defendant denied. The jurists do not yet mention the actio in duplum and substantively follow justinianic law. The second remedy we particularly find in late Byzantine law. In the period between the early and late Byzantine law Basilica remarks of jurists can be found who display a move from the actio legis Aquiliae with litiscrescense unto an independent actio in duplum. Because of contradictions, mistakes and differences of opinions no clear explanation for the development of the actio legis Aquiliae (utilis) and the actio in factum to an actio in duplum can be discovered.