The number of subjects to be found on any one vase is of course usually limited to one, two, or at most three, according to the shape. Usually when there is more than one the subjects are quite distinct from one another; though attempts have been made in some cases, as in the B.F. amphorae, to trace a connection.[30] On the other hand, the R.F. kylikes of the strong period often show a unity of subject running through the interior and exterior scenes, whether the theme is mythological or ordinary.[31] It was only in exceptional cases that an artist could devote his efforts to producing an entire subject, as on some of the large kylikes with the labours of Theseus,[32] or the vases representing the sack of Troy.[33] The great François vase in Florence is a striking example of a mythology in miniature, containing as it does more than one subject treated in the fullest detail. And here reference may be made to the main principles which governed the method of telling a story in ancient art, and prevailed at different periods.[34] The earliest and most simple is the _continuous_ method, which represents several scenes together as if taking place simultaneously, although successive in point of time. This method was often employed in Oriental art, but is not found in Hellenic times; it was, however, revived by the Romans under the Empire, and prevailed all through the early stages of Christian art. Secondly, there is the _complementary_ method, which aims at the complete expression of everything relating to the central event. The same figures are not in this case necessarily repeated, but others are introduced to express the action of the different subjects, all being collected in one space without regard to time, as in the continuous style. This is of Oriental origin, and is first seen in the description of Achilles’ shield; it is also well illustrated in the François vase, in the story of Troilos. Here the death of Troilos is not indeed actually depicted, but the events leading up to it (the water-drawing at the fountain and the pursuit by Achilles) and those consequent on it (the announcement of the murder to Priam and the setting forth of Hector to avenge it) are all represented without the repetition of any figures. Lastly, there is the _isolating_ method, which is purely Hellenic, being developed from the complementary. This is best illustrated by the Theseus kylikes, with their groups of the labours, which, it should be remembered, are not continuous episodes in one story, but single events separated in time and space, and collected together with a sort of superficial resemblance to the other methods.