Large parts of the text are missing: especially from the 4th and the 5th book only minor fragments survived. All other books have at least some passages missing. "Scipio's dream", which is only a part from the 6th book, is nearly all that survives from that book. The "Somnium Scipionis", as it is known, survives because it was the subject of a commentary by Macrobius, who excerpted large portions; both he and his readers in the Middle Ages and Renaissance were mainly interested in its discussion of astrology and astronomy, especially given the loss of the rest of the book. An enterprising copyist early in the textual tradition appended a copy of the "Somnium" to a copy of Macrobius's Commentary, but this copy appears to be inferior to the one Macrobius was reading. This text became so popular that its transmission was polluted by multiple copies; it has been impossible to establish a stemma for it.