The article is dedicated to the identification of the content of MS. Slav. 321 from the Library of the Romanian Academy of Sciences in Bucharest. The codex is in a very bad condition, significantly affected by damp, the letters are blurred and faded, and the text can be read only with great difficulty. The detailed investigation of the watermarks revealed that it most probably originated during the last decade of the 14th century. According to A. Jacimirskij, who first studied the manuscript, it comprised the Chronicle of George Hamartolos (the so-called Letovnik). Compiling the list of the existing Slavic transcripts of the Hamartolos’ Chronicle, M. Weingart literally repeated Jacimirskij’s information. Jacimirskij’s identification was reiterated in all the existing catalogues (such as those by P. Panaitescu and I. R. Mircea) and, with a reference to Weingart, the manuscript has been counted among the Slavic copies of Hamartolos’ Chronicle in numerous dictionaries and studies of medieval Slavic literature. The collation of the text of MS. Slav. 321 (where it could be read without the aid of technical devices) with the facsimile edition of the Letovnik , however, proved that MS. Slav. 321 incorporated the Slavic translation of another Byzantine chronicle – the Chronicle of John Zonaras. The mistake in the identification of the text made by Jacimirskij is understandable, since the works of George the Monk and John Zonaras have much in common and are usually regarded as “exemplary monk’s chronicles.” Furthermore, MS. Slav. 321 provokes special interest. First, this is the earliest known transcript of the Slavic translation of Zonaras’ Chronicle. Its examination in comparison with the rest of the existing transcripts could shed additional light on the problems as to when and where the Slavic translation was undertaken. Second, the marginal notes and glosses (later or contemporary to the main text), traces of which survive on different folia – some of them related to historical events or to the process of the translation of this particular piece of work – are of particular value and should be studied separately. Their existence in the Bucharest codex suggests that often information on historical events was recorded in books of historical content, thus registering what scribes and readers considered important and worth remembering, in this way making it a part of world history.