He was in the retinue of Bishop Absalon, who encouraged him to write the monumental history of Denmark (Gesta Danorum); he completed it in 16 books between 1216 and 1219, in a Latin style modeled on that of Valerius Maximus, Justin, and Curtius Rufus (and in the poetic parts of the work, there are also reminiscences of Horace and Virgil). He recounts the history from biblical times to 1187 AD (the subjugation of the Wends by the Danes), with the dual purpose of inspiring young people with tales of their ancestors' deeds and of making Denmark known to the world. For the first nine books, S. draws extensively on the common Germanic saga heritage and his own imagination; for the later books, he relies on oral tradition and whatever information he could gather. At the center of the work is the figure of Absalon, a Viking and bishop, warrior and servant of the Lord; S. is more a narrator than a historian in the modern sense of the word; Roman, or at least classical, is his sense of the State, which blends with the innate loyalty to the king in him. Some have wished to see in him a personal anti-ecclesiastical stance, but his work merely reflects the free aristocratic attitude of the Danish high clergy at the time of Valdemar, when one could «equally well honor God by fighting the enemies of the faith as by attending to divine service». The work enjoyed success among contemporaries and posterity.
Particularly felicitous in spiritual congeniality, if not in textual fidelity, is the translation by Grundtvig (1783–1872); the first Danish translation, by A. S. Vedel, dates to 1575. All editions derive from the princeps edition published in Paris in 1514 by Christiern Pedersen, since the most complete manuscript has been lost (much of the text survives in a manuscript found in Angers in 1863, now in Copenhagen; other fragments are in a 14th-century manuscript at the Rigsarkivet in Copenhagen).