 The oldest narrative source mentioning him briefly is Adam of Bremen's "Gesta Hammaburgensis ecclesiae pontificum" of "circa" 1070.In the 1190s, two Latin versions of ""Óláfs saga Tryggvasonar"" were written in Iceland, by Oddr Snorrason and by Gunnlaugr Leifsson - these are now lost, but are thought to form the basis of later Norse versions.Snorri Sturluson gives an extensive account of Olaf in the "Heimskringla" saga of "circa" 1230, using Oddr Snorrason's saga as his primary source.