Which Equinox? ANTONIO CÉSAR GONZÁLEZ-GARCÍA AND JUAN ANTONIO BELMONTE Abstract Resumen The reform of the Republican calendar intro- La reforma del calendario Republicano intro- duced by Julius Caesar in 46 B.C. was carried ducida por Julio César en el 46 a. de C. se llevó out to adjust the year and festivities to the sea- a cabo par ajustar el año y las festividades con sons. There are varying definitions for equinox, las estaciones. Existen varias posibles defini- and historians have generally accepted that ciones de equinoccio y los historiadores han March 25 was the canonical date for the vernal admitido an general que el 25 de Marzo era equinox. We find that the sense of equinox used la fecha canónica para el equinoccio vernal. could have been the day that marked the middle Nosotros encontramos que la definición de of the interval between the winter and summer equinoccio que pudo ser utilizada fue la de el solstices. A method of deriving these dates is día que marca la mitad en el intervalo entre suggested. This also implies that from the be- los solsticios de invierno y verano. Se sugiere ginning of Caesar’s reform, the length of the un método para obtener dicha fecha. Esto im- months, especially February (Februarius) and plica que la longitud de los meses, en especial August (Sextilis), was the same as it is now. Febrero (Februarius) y Agosto (Sextilis) fue la misma que ahora desde el inicio de la reforma juliana. Our calendar is basically the same that Julius Januarius, Februarius, Martius, Aprilis, Maius, Caesar set in place in 46 B.C. The subject of the Junius, Quinctilis, Sextilis, September, October, present study is Caesar’s reform of the Roman cal- and . Four months had 31 November, December endar. According to classical sources(Suetonius De days (Martius, Maius, Quinctilis, and October), vita Caesarum, divus Iulius [hereafter Iul.] 40.1), seven had 29, and Februarius had 28, amounting Caesar reformed the calendar to bring the festivities to a total of 355 days in a year. To adjust this year back into agreement with the seasons, in particular to the tropical solar year, the Romans introduced an with the equinox (Mommsen 1981:62 [1859]). intercalary month (mensis intercalaris) every two years. The intercalation was performed by reduc- The Roman Republican Calendar ing February to 23 or 24 days and intercalating a The Roman Republican calendar had 12 months: month of 27 days (Michels 1967:16). A college of Antonio César González-García is a Researcher at the Universidad Autónoma de Madrid. His main research field is galactic dynamics and galaxy interactions. He also does investigations in cultural astronomy and archaeoastronomy, with interests ranging from megalithic monuments to the Punic and Roman cultures. Juan Antonio Belmonte is a Researcher at the Instituto de Astrofísica de Canarias, where he teaches history of astronomy and archaeo- astronomy and investigates stellar physics and cultural astronomy. He has been Director of the Science and Cosmos Museum of Tenerife from 1995 to 2000 and is currently the President of the European Society for Astronomy in Culture (SEAC). He is the author or coauthor of numerous books and papers on the archaeoastronomy of Mediterranean cultures. © 2006 by the University of Texas Press, P.O. Box 7819, Austin, TX 78713–7819 VOLUME XX 2006 95 priests called the pontifices had among their duties convincingly that it could not have been later than the care of the calendar. the end of the fifth century and that the most prob- This calendar with 355 days was clearly lunar able time was the period of the decemviri around based and could have been based on an earlier 450 B.C., at a time when the young Republic was luni-solar calendar. However, the fact that there setting its institutions in place. Michels also points were months with 31 days and that the intercalation out that such a date leaves ample time to have earlier aimed to bring the year closer to the solar one means used a lunar or luni-solar calendar, perhaps with a a break with the lunar calendar. Although for some different beginning of the year, probably in March, authors this was the first calendar in antiquity to be which was later regarded as traditional. independent of the Moon (Michels 1967:16), recent The names of the last six months as numerals and evidence indicates that the Egyptians had just one the spring rites performed during March, together calendar of 365 days (Belmonte 2003). with the memory of an earlier beginning of the year The exact date for the beginning of the year has in this month, seem to point toward a previous cal- been quite controversial. Mommsen (1981 [1859]) endar in which the year started in March, close to the thought that the start of the year had been March vernal equinox. The ancient sources also mention until the time of Caesar. However, after the dis- that the first calendar started in March. Accord- covery of the Fasti Antiates Maiores, a calendar ing to Macrobius (Sat. 13.3), Censorinus (De die from Republican times, in which the year begins on natali 22.13), and Plutarch (Numa 18.3, 19.2), the January 1, this view was no longer regarded as pos- first Roman calendar was established by Romulus, sible. Scaliger had proposed that before the period the legendary founder of Rome. The year began in between the Lex Aelia and the Lex Fufia, around 153 March in the spring equinox, and the last month B.C., the start of the year had been changed from was December. Lydus (De mensibus 3.22; Michels March 1 to January 1 (Michels 1967:97n10). After 1967:99) refers to an ecclesiastical beginning of the 153 B.C. the consuls started their rule on January year in January and a traditional one in March. 1, whereas they had previously started at different Since the fifth century B.C., when the decemviri times of the year. This view had a number of follow- reformed the calendar, it had been up to the pontifices ers; however, we must keep in mind that the start of to keep it in accordance with the seasons. This re- the civil and consular years did not always have to form lasted until the time of Julius Caesar. However, 1 be the same. According to the classical sources, the bribery and corruption were apparently common. To year originally started in March, but quite early, still prolong their term of office, magistrates would ad- in the kingdom period (with King Numa according vise the pontifex to extend the year further. On other to some sources or with Servius Tullius [Michels occasions, the senators might suggest a shorter year 1967:210]), the year’s beginning was changed to to curtail the rule of certain magistrates. Also, the January 1. It is thus now widely accepted that the intercalary period was a time of bad omens, and it ap- Republican calendar always started January 1. pears that during the Punic Wars this period was not Exactly when the Republican calendar was introduced (Macrobius Sat.; see Michels 1967:102). implemented is also a matter of debate. According These practices made the Roman calendar quite cha- to Hartmann (Michels 1967:210), it was by the time otic and often rendered the calendar out of step with of Servius Tullius that the basic rules of the calen- the seasons. It even made a subjective issue of when dar were established, a view supported by Gjerstad festivities should be celebrated (see, e.g., Richards (Michels 1967:217). Belloch, on the contrary, 1998:208; for a discussion on the Roman calendar thinks that until Flavius published his Fasti in 304 during the Republic, see Michels 1967). B.C., the calendar was not independent of the Moon (Michels 1967:211). For Michels (1967:121–129) Caesar’s Reform the pre-Julian calendar was devised and started at In the first book ofDe vita caesarum, Suetonius tells the time of the decemviri in 450 B.C. Michels argues us that Julius Caesar, who had been named pontifex 96 ARCHAEOASTRONOMY maximus in 63 B.C., reformed the calendar to bring (1997) points out that many studies suffer from a the festivals in accordance with the seasons (Pliny preconception of the term equinox. One has there- Naturalis historia [hereafter HN] 18.57.214; Plu- fore to be careful when using the term equinoctial tarch Caesar 59.1–6; Suetonius Iul. 40.1). Caesar alignment and be aware whose equinox we are talk- decreed that the year should have 365 days, with the ing about when reaching certain conclusions. addition of an extra day every four years in order For some historical cases there is written evi- to bring the calendrical year into closer proximity dence for the use of the term equinox. We might to the tropical year. This system had the advantage then go further and ask which equinox is referred of everything being fixed and obviated the need for to. Following Ruggles (1997), various meanings of subjective decisions from the pontifices concerning equinox could be used. the calendar. Caesar also decreed that the year 708 A first definition might be the time when the A.U.C. (ab urbe condita, or from the founding of the sun crosses the celestial equator, at which instant city, 46 B.C.) should have an extra 90 days, includ- it has a declination of δ = 0°. This is the present- ing one mensis intercalaris and two extra months day definition for equinox. Second, one may have between November and December (Suetonius Iul.