Herodotus wrote down a very brief account of the history of Assyria in his Histories, but he promised to deliver a complete logos as well. We can find two remarks on this future project that (possibly) never materialized in the end. In the preserved text, there are only several mentions of Assyrian kings, history, and customs, but it seems he planned to expand the narrative further, potentially in a separate piece of work. The result was a mysterious Assyrian logos. In this article, I will explore the possible influence of Herodotus' account on the Greek tradition about this eastern land through either one of these logoi, if, in fact, he had any at all. In the first part, I will examine the sources, whether they refer to his more detailed treatise on Assyria, and what can be said about this work in general. In the second part, I will focus on his extant Assyrian logos, whether any later author (most notably Ctesias and Berossus) could have used his work as a source, and who became the authorities on the history of Assyria, considering the changes in the narratives.