On the ancient Roman calendar, mensis Iunius or Iunius, also Junius (June), was the fourth month, following Maius (May). In the oldest calendar attributed by the Romans to Romulus, Iunius was the fourth month in a ten-month year that began with March (Martius, "Mars' month"). The month following June was thus called Quinctilis or Quintilis, the "fifth" month. Iunius had 29 days until a day was added during the Julian reform of the calendar in the mid-40s BC. The month that followed Iunius was renamed Iulius (July) in honour of Julius Caesar.
Name of the month
In his poem on the Roman calendar, Ovid has three goddesses present three different derivations of the name Iunius. Juno asserts that the month is named for her. Juventas ("Youth") pairs Iunius with Maius: the former, she says, comes from junior, "a younger person", in contrast to maiores or the "elders" for whom May was named. Juno's own name may derive from the same root meaning "young", and these two possibilities may be reconcilable. Ovid has Concordia claim that Iunius comes from iungo, iunctus, "join", in honor of her uniting the Romans and the Sabines. Elsewhere, an even less likely derivation relates the month name to Marcus Iunius Brutus, a member of the gens Iunia who made the first sacrifice to Dea Carna on the Kalends (June 1).
Month illustrations that draw on the Calendar of Filocalus (354 AD) show a nude male holding a torch that may be an allegory of the summer solstice. Solstitium is noted on June 24 of the calendar. The torch may be a reference to dies lampadarum, "day of torches", variously interpreted as the sun's rays or as the torch of Ceres, the grain goddess who carried a torch while searching for her abducted daughter Proserpina. The solstice marked the beginning of the harvest, which is represented by the basket of fruit and a sickle. The plant may be a bean, since June 1 was the "Bean Kalends".
The Romans did not number days of a month sequentially from the 1st through the last day. Instead, they counted back from the three fixed points of the month: the Nones (5th or 7th, depending on the length of the month), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Nones of June was the 5th, and the Ides the 13th. Roman counting was inclusive; June 9 was ante diem V Idūs Iunias, "the 5th day before the Ides of June," usually abbreviated a.d. V Id. Iun. (or with the a.d. omitted altogether). The last day of June was the pridie Kalendas Quinctilis (pridie Kalendas Iulias after July was renamed), "day before the Kalends of July". The modern equivalent of this date was June 29 on the pre-Julian calendar, but June 30 on the Julian, because June was one of the months to which a day was added in realigning with astronomical time. June 23 was thus VIII Kal. Quinct., "the 8th day before the Kalends of Quinctilis", during the Republican era, but IX Kal. Iul., "the 9th day before the Kalends of July", in the Imperial era.
On the calendar of the Republic and early Principate, each day was marked with a letter to denote its religiously lawful status. In June, these were:
- F for dies fasti, days when it was legal to initiate action in the courts of civil law;
- C for dies comitalis, a day on which the Roman people could hold assemblies (comitia), elections, and certain kinds of judicial proceedings;
- N for dies nefasti, when these political activities and the administration of justice were prohibited;
- NP, the meaning of which remains elusive, but which marked feriae, public holidays.
By the late 2nd century AD, extant calendars no longer show days marked with these letters, probably in part as a result of calendar reforms undertaken by Marcus Aurelius. The unique Q.ST.D.F. of June 15 stands for Quando stercum delatum fas, when it was a religious obligation to remove dirt from the Temple of Vesta. Varro specifies the act of sweeping (everritur).
Festivals marked in large letters on extant fasti, represented by festival names in all capital letters on the table, are thought to have been the most ancient holidays, becoming part of the calendar before 509 BC. A dies natalis was an anniversary such as a temple founding or rededication, sometimes thought of as the "birthday" of a deity. 
Unless otherwise noted, the dating and observances on the following table are from H.H. Scullard, Festivals and Ceremonies of the Roman Republic. Scullard places the Taurian Games on June 25–26 on a five-year cycle, but other scholars believe these ludi had no regular date and were held as a crisis ritual when needed. After the Ides, dual dates are given to represent both the earlier calendar, when June had 29 days and July was called Quinctilis, and the 30-day month of the Julian calendar.
|June 1||Kalendae Iuniae||N||• dies natalis of the Temple of Juno Moneta
• dies natalis of the Temple of Mars outside the Porta Capena
• dies natalis of the Temple of the Tempestates
• festival of Carna, popularly known as the "Bean Kalends", and in the later Empire the last day of the Ludi Fabarici ("Bean Games")
|2||a.d. IV Non. Iun.||F|
|3||III Non. Iun. ||C||• die natalis of the Temple of Bellona in the Circus Flaminius|
|4||prid. Non. Iun.||C||*dies natalis of the Temple of Hercules Magnus Custos ("Hercules the Great Watchman") near the Circus Flaminius, with ludi added in the Imperial era|
|5||Nonae Iunias||N||• dies natalis of the Temple of Dius Fidius|
|6||VIII Id. Iun.||N||• Colossus coronatur: the colossal statue of Sol was wreathed (Imperial era)|
|7||VII Id. Iun.||N
|• Vesta aperitur ("Vesta is opened"), when the inner sanctum of the Temple of Vesta was opened for women only
• Ludi Piscatorii, "Fishermen's Games"
|8||VI Id. Iun.||N
|• dies natalis of the Temple of Mens|
|9||V Id. Iun.||N
|10||IV Id. Iun.||N|
|11||III Id. Iun.||NP
•dies natalis of the Temple of Fortuna in the Forum Boarium
|12||prid. Id. Iun.||N|
|• monthly Feriae Iovi
• Lesser Quinquartus
|14||XVII Kal. Quinct.
XVIII Kal. Iul.
|15||XVI Kal. Quinct.
XVII Kal. Iul.
|• Vesta clauditur, inner sanctum of Vesta closed|
|16||XV Kal. Quinct.
XVI Kal. Iul.
|17||XIV Kal. Quinct.
XV Kal. Iul.
|18||XIII Kal. Quinct.
XIV Kal. Iul.
|19||XII Kal. Quinct.
XIII Kal. Iul.
|C||• dies natalis for the Temple of Minerva on the Aventine|
|20||XI Kal. Quinct.
XII Kal. Iul.
|C||• dies natalis for the Temple of Summanus near the Circus Maximus|
|21||X Kal. Quinct.
XI Kal. Iul.
|22||IX Kal. Quinct.
X Kal. Iul.
|23||VIII Kal. Quinct.
IX Kal. Iul.
|24||VII Kal. Quinct.
VIII Kal. Iul.
|C||• dies natalis for the Temple of Fors Fortuna across the Tiber
• Solstice or dies lampadarum
|25||VI Kal. Quinct.
VII Kal. Iul.
|26||V Kal. Quinct.
VI Kal. Iul.
|27||IV Kal. Quinct.
V Kal. Iul.
|C||• dies natales for a Temple of the Lares and of Jupiter Stator on the Palatine|
|28||III Kal. Quinct.
IV Kal. Iul.
|29||prid. Kal. Quinct.
III Kal. Iul.
|30||prid. Kal. Iul.||C|
- H.H. Scullard, Festivals and Ceremonies of the Roman Republic (Cornell University Press, 1981), p. 126.
- Michele Renee Salzman, On Roman Time: The Codex Calendar of 354 and the Rhythms of Urban Life in Late Antiquity (University of California Press, 1990), p. 92.
- The month name is construed as an adjective modifying Kalendae, Nonae or Idūs, all of which are of feminine grammatical gender.
- Salzman, On Roman Time, pp. 17, 122.
- Varro, De lingua latina 6.32; Robin Lorsch Wildfang, Rome's Vestal Virgins (Routledge, 2006), p. 140; Salzman, On Roman Time, p. 160.
- Jörg Rüpke, The Roman Calendar from Numa to Constantine: Time, History, and the Fasti, translated by David M.B. Richardson (Blackwell, 2011, originally published 1995 in German), p. 6.
- Scullard, Festivals and Ceremonies of the Roman Republic, p. 41.
- Scullard, Festivals and Ceremonies, pp. 126–158.
- Salzman, On Roman Time, p. 122.
- Abbreviated form of ante diem IV Nonas Iunias, "fourth day before the Nones of June".
- Abbreviated form of ante diem III Nonas Iunias.
- Abbreviation of pridie Nonas Iunias, "day before the Nones of June".
- Salzman, On Roman Time, p. 126.
- Abbreviated form of ante diem VIII Idūs Iunias, with the ante diem omitted altogether from this point.
- Salzman, On Roman Time, pp. 151, 125.
- Abbreviation of pridie Idūs Iunias, "day before the Ides of June".
- Abbreviated form of ante diem XVII Kalendas Iunias.
- Marked on the Calendar of Filocalus; Salzman, On Roman Time, pp. 92–93, 124.