Anonymus Leidensis is the conventional designation of the anonymous author of the 9th-century Latin geographical treatise De situ orbis ("On the Location of the Earth").
[3] He claims to be writing at the request of his fellow monks and his students, who wanted a better understanding of the recent Viking raids that penetrated the interior of Gaul from the Mediterranean via the rivers.
[4] According to him, although the Earth's features can be perceived "by both the corporeal eyes and the internal mental glance", he gives pride of place to the latter—intellectual apprehension—and thus to written authorities.
[2] It is based not on experience, but on written sources, including Mela, Isidore, Martianus Capella, Aethicus Ister, Julius Solinus and Paulus Orosius.
[9] The term "Leidensis" refers to the location of the only known copy of De situ, which is now in the Leiden University Library.