The writing by Athanasius unanimously transmitted in the manuscripts under the title Apologia ad Constantium is generally dated to the period of his third exile (356–361). Athanasius defends himself against accusations apparently laid against him by the Emperor and seeks in this way to justify his flight. The text is in several respects problematic and reflects editorial interference at various places. The unity of the text has long been debated between various opinions, generally resulting in the conclusion that the document was reworked in two or three phases. There is indeed a recognisable break between chapters 26 and 27. The thesis in this article is that the Apologia ad Constantium as we have it today is a compilation of two originally independent letters to the Emperor. The first letter (chs. 1–26), whose conclusion is now lost, dates from the beginning of the third exile; the second (chs. 27–35) – the beginning is missing and its extent can no longer be determined – probably dates from the year 358. It is no longer possible to establish whether the compilation was brought about by deliberate editorial action or through the accidental loss of pages.