Genesis and outlook

Trismegistos Time (formerly Trismegistos Calendar) is a relatively new section that came about as a result of Sofie Remijsen’s interest in the practical significance of Sunday for the early Christians. Sofie wanted to make her conversion lists publicly available, and Mark Depauw offered to do that in the framework of Trismegistos. Then the idea came to link the list of days to the dates in Trismegistos, and this is how TM Calendar was born, initially for the period 800 BC - AD 800. Afterwards collaboration with the Altägyptische Kursivschriften (AKU) project in Mainz (and indirectly with other egyptological projects - see below) led us to expand the chronological scope to 3500 BC - AD 1000.

TM Time - which is mostly limited to Egypt - has benefited a lot from taking part in the GODOT project, which aims to be an all-encompassing project to time and dates for the whole of the ancient world. It was in the framework of GODOT that we were able to model the various tables in our chronological database, and enter the preserved ancient dates in all BGU texts and P. Oxy. volumes (the latter not yet available online). We hope one day soon to expand this to all papyrological and afterwards also epigraphic texts.

Despite all this work, TM Time is still in its initial phase. The stable identifiers are still under construction conceptually (see below). Right now it should be seen as a tool to convert dates from old calendar systems to new and vice-versa, which also facilitates finding texts dated to specific periods in Trismegistos. We hope one day perhaps also to work together with other projects such as PeriodO.

What is a date?

For TM a date is a specific period of time connected to an event or text. Since time is (for our purposes at least) a linear progression, we have to choose a basic unit to measure it. We have opted for the day, as a lower granularity would enormously complicate counting without sufficient added benefit, given that in the ancient world only very few dates refer to smaller units than the day.

Working with traditional dating system with years, months and days is allright for humans, but for database purposes, we needed a simple number to refer to a unique day. Being blissfully unaware of the Julian day numbers used in astronomy, we have developed our own system with 1 January 333 BC as day 1, a serial number which increases by 1 for each day. For dates preceding 1 January 333 BC, we substract 1, starting with 0 for 31 December 334, and continuing with negative numbers for what precedes.

A period of time can thus be identified by a combination of two day numbers with an underscore ('_') in this system: thus refers to 25 March 332 BC, and (TM Time 135019_135383) to the period from 29 August 37 AD to 28 August 38 AD. The latter can in Egypt also be described as '(regnal) year 2 of Caligula', which we have also given a persistent identifier: or TM Period 538. For eponyms, we have for the time being still separate stable identifiers, e.g. TM Eponym 36 ( for Caligula, although this may change in the future (we will make sure to put a redirect in place, of course). If there is a period (or eponym) identifier to your taste, it is better to use that as that is the chronological concept that humans generally refer to. In the case of centuries, for example, our 6th century AD is TM Period 3022, which currently corresponds to TM Time 303889_340413 (being 1 January 500 to 31 December 599). This 'alternative' conversion of a century goes back to the very earliest stages of the database, long preceding TM. We may well correct it to 1 Jan 501 - 31 Dec 600 in the future, but first want to wait for general scholarly conventions on how to deal with dates such as 'early second century AD' (TM Period 2720), for which about every single project has its own conversion into numbers.

The TM Time and TM Period identifiers refer to chronological concepts. This is also the level at which GODOT works, and we are implementing their stable identifiers now. There is, however, also another level at which we use persistent identifiers: that of the chronological expression as it is found in the ancient source itself. We have developed these in the course of the GODOT project and the top levels are already accessible in this version of TM Time, be it only through the 'Dates'-tab on the detail pages of TM Texts. An example is TM ChronNam 541 ( for the chronological concept '(regnal) year 6', independent from its application to a specific ruler. This entry in our CHRONNAM table is connected with several CHRONNAMVAR entries and in the level below that with CHRONNAMVARCASE entries. The latter levels are currently still inaccessible, but we hope to change that once we continue our work on TM Time, hopefully in the context of GODOT. Above that we are working on a CHRONNAMCOMB level, which will contain combinations of chronological entities, again purely on the formal level.

I am sure the last word has not been said about modelling dates, and we would be happy to discuss this with anyone interested.

Chronological background

Reigns and regnal years

The regnal years follow the Egyptian count: the second regnal year starts on 1 Thot after the accession of the new emperor. The first and last regnal years are therefore often incomplete calendar years. Because of the uncertainty of accession dates, there might be an overlap between the reigns of successive emperors.

For Ancient Egypt before the late pharaonic period (specifically before the 24th Dynasty), the information is based on a list resulting from work done in Leipzig by the Thesaurus Linguae Aegyptiae (TLA), with some modifications by the project Altägyptische Kursivschriften (AKU). This was compiled by Lutz Popko (with the assistance of Ines Köhler for the period until the Old Kingdom). Of course many of these dates are only approximate. That they look so precise is the result of their purely pragmatic function, i.e. to create a list of pharaohs. Originally, they were never meant to be shown, and certainly not to be presented as a new chronological model.

For late pharaonic Egypt, our information are the chronological tables of Pestman in his P. Tsenhor. This is a purely pragmatic decision, and we realize that certainly before the advent of the 26th dynasty, the dates are approximate at best. We are considering adopting the reconstruction of TLA/AKU instead, but as this would involve changing the dates for many abnormal hieratic texts, we have so far refrained from doing so.

The Ptolemaic regnal years are based of “Theodore C. Skeat, The Reigns of the Ptolemies, München 1969”. This information was updated on the basis of “M. Depauw et al., Chronological Survey of Demotic and Abnormal Hieratic Sources, Version 1.0 February 2007, Köln and Leuven 2008” and the chronological details examined by the late Chris Bennet on his website.

The reigns of the Roman emperors are based mostly on: “P.W. Pestman, Chronologie égyptienne d’après les textes démotiques, Leiden, 1967” and “R.S. Bagnall and K.A. Worp, Chronological Systems in Byzantine Egypt, Leiden, 2004” for late antiquity.


Egyptian era years start from Thot 1.

The Diocletian era or Era of the Martyrs was in use from the fourth century AD onwards. Year 1 is AD 284, the first regnal year of Diocletian. The continuation of Diocletian’s regnal years after his death offered a solution to the confusion created by tetrarchy for the count of regnal years. The era is used for dating especially in Arsinoites and Herakleopolites. The era was later renamed ‘the era of the martyrs’ by Christians.

The Oxyrhynchos era (coming soon) was used only in Oxyrhynchus and contains two year numbers: X/X-31. The first number is a continuation of the regnal years of Constantius II, the second number a continuation of the regnal years of Julian.

NOTE: In the mid-fourth century (337-350s), papyri from Oxyrhynchus temporary use an era continuing the regnal years of Constantine I. To convert such a date, fill out only year 1.


The Egyptian indiction normally started in the beginning of the harvest (1 Pachon = 26 April), when the praedelegatio (preliminary tax rates) was issued.

There are many exceptions to this rule:

  • A date around 1 Pachon: The indiction is not always calculated exactly from 1 Pachon. According to the Roman calendar, the Egyptian indiction started on 1 May = 6 Pachon. Check whether the text specifies with the words ἀρχῇ en τέλει which indiction is meant. When the text speaks of the end of the indiction in the beginning of Pachon, add one year to the Julian date given by the converter.

  • Documents from the Arsinoites: Because the final tax scheme was issued in Epeiph, an indiction starting on 1 Epeiph was in use for chronological purposes in the Arsinoites. If you are dealing with a document from Arsinoites, which is not concerned with taxes and is dated to Pachon or Pauni, add one year to the Julian date given by the converter.

Look for a Thoth indiction, if you are dealing with:

  • Documents from AD 312-327: In period 312-327, the indiction started after the harvest, together with the Egyptian civil year on 1 Thoth (= 29 Augustus).

  • Documents from Oxyrhynchus: There was a tendency to equate indiction year with the civil year, especially in Oxyrhynchus and possibily in the Herakleopolites.

  • Non-Egyptian documents: Outside of Egypt, the indiction started on 23 September in the fourth and early fifth century. It shifted to 1 September in the second half of the fifth century, perhaps in 462, but only in the Eastern Roman Empire. If your non-Egyptian document falls between 29 August and 1 or 23 September, add one year to the Julian date given by the converter.

For more information see R.S. Bagnall and K.A. Worp, Chronological Systems of Byzantine Egypt, 2nd edition (Leiden and Boston 2004).

Consular dates (30 BC and after)

Our information is based on A. Degrassi, I fasti consolari dell’impero romano dal 30 avanti Cristo al 613 dopo Cristo, Roma 1952, and R.S. Bagnall, A. Cameron, S.R. Schwartz and K.A. Worp, Consuls of the Later Roman Empire, Atlanta 1987.

New moon dates (400 BC - AD 1000)

Our information is based on the calculations of Fred Espenak, available online on The tables are in Universal Time there, and we have added 2 hours 2 minutes for Alexandria.

How to cite

Please consult this page.


In its present stage, Trismegistos Time is a tool for Egypt in the sense that all calendar indications refer to Egyptian calendar systems (with exception of Roman consular dates). As it comes to the tables of which the database exists, the most important distinction is that between dates on which texts were written (DATE) and dates mentioned in documents (DATEREF). Since all documents in TM have been assigned a date - even if this is sometimes a very broad one spanning the entire period TM covers - all texts in the database can be accessed through the DATE table.
For TM Dateref, the database with attestations of dates mentioned in the ancient sources, we currently only cover Egypt's Greek papyrological texts, in casu BGU documents (available online) and P. Oxy. texts (not accessible online yet). We hope to expand our coverage in the not too distant future.


A database of chronological aspects of texts from the ancient world.
General coordination: M. Depauw, S. Remijsen
Database structure (Filemaker 12-18): M. Depauw
Online version (PHP & MySQL): M. Depauw
Online version (web design): Y. Broux
Data processing: S. Remijsen (calendrical lists), H. Verreth (mentioned dates)