Zodiacal and Planetary 'decani'. The 36 ecliptical 'decani' (sectors of 10°) were distributed either to the twelve zodiacal signs or to the seven planets. The first system has been transmitted only by the Roman didactic poet Manilius, who commits an error at the end of his catalogue that can be explained by comparing it with the more frequent planetary one. Both systems follow the Roman calendar beginning with the Ram respectively Mars. Although the zodiacal system (36 : 12) runs without remainder whereas the planetary one (36 : 7) repeats Mars once more (six times), so that it both begins and ends with this planet, this planetary system prevails. Four possible astrological reasons of this contradiction are discussed including other texts, mostly taken from the 'Babylonian' Teucrus (at the latest first century BC), who represents the first witness, if not the inventor of this particular lore.