Livy, Ab Urbe Condita, Book I, Chapters 4–35 (trans. B.O. Foster, Loeb Classical Library; trans. A. de Sélincourt, Penguin Classics, The Early History of Rome, 1960)
Dionysius of Halicarnassus, Roman Antiquities, Books I–III
Plutarch, Life of Romulus; Life of Numa
Cicero, De Re Publica, Book II.12–33 — Cicero's survey of the first four kings
Ovid, Fasti, Books I–VI — on the Roman calendar and its religious associations
Festus, De Verborum Significatu — valuable for archaic religious institutions
Secondary Sources
T.J. Cornell, The Beginnings of Rome (Routledge, 1995), Chapters 5–9 — essential on the regal period
Gary Forsythe, A Critical History of Early Rome (University of California Press, 2005), Chapters 4–5
Robert Ogilvie, A Commentary on Livy, Books 1–5 (Oxford University Press, 1965) — detailed commentary on the primary text
Mary Beard, SPQR: A History of Ancient Rome (Profile Books, 2015), Chapter 3
On Roman Religion and Numa's Institutions
John Scheid, An Introduction to Roman Religion (Indiana University Press, 2003)
Mary Beard, John North, and Simon Price, Religions of Rome, Vol. I (Cambridge University Press, 1998) — the standard scholarly survey
Georg Wissowa, Religion und Kultus der Römer (Munich, 1912) — foundational, though dated
On the Vestal Virgins
Ariadne Staples, From Good Goddess to Vestal Virgins: Sex and Category in Roman Religion (Routledge, 1998)
Robin Lorsch Wildfang, Rome's Vestal Virgins (Routledge, 2006)
On the Horatii and Curiatii
Livy I.23–26 — the primary account
The story's historicity is discussed in Cornell, Beginnings, pp. 116–118, and Ogilvie, Commentary, pp. 107–116
On Just War
W.V. Harris, War and Imperialism in Republican Rome (Oxford University Press, 1979) — essential on Roman warfare and its ideology
Coleman Phillipson, The International Law and Custom of Ancient Greece and Rome, Vol. II (Macmillan, 1911) — dated but thorough on ius fetiale
On Ostia
Russell Meiggs, Roman Ostia (Oxford University Press, 2nd ed., 1973) — the standard work; dates the earliest significant archaeological evidence to the 4th century BCE
Fausto Zevi (ed.), Ostia, 2 vols. (Banco di Roma, 1996)
Livy, Ab Urbe Condita, Book I, Chapters 4–35 (trans. B.O. Foster, Loeb Classical Library; trans. A. de Sélincourt, Penguin Classics, The Early History of Rome, 1960)
Dionysius of Halicarnassus, Roman Antiquities, Books I–III
Plutarch, Life of Romulus; Life of Numa
Cicero, De Re Publica, Book II.12–33 — Cicero's survey of the first four kings
Ovid, Fasti, Books I–VI — on the Roman calendar and its religious associations
Festus, De Verborum Significatu — valuable for archaic religious institutions
Secondary Sources
T.J. Cornell, The Beginnings of Rome (Routledge, 1995), Chapters 5–9 — essential on the regal period
Gary Forsythe, A Critical History of Early Rome (University of California Press, 2005), Chapters 4–5
Robert Ogilvie, A Commentary on Livy, Books 1–5 (Oxford University Press, 1965) — detailed commentary on the primary text
Mary Beard, SPQR: A History of Ancient Rome (Profile Books, 2015), Chapter 3
On Roman Religion and Numa's Institutions
John Scheid, An Introduction to Roman Religion (Indiana University Press, 2003)
Mary Beard, John North, and Simon Price, Religions of Rome, Vol. I (Cambridge University Press, 1998) — the standard scholarly survey
Georg Wissowa, Religion und Kultus der Römer (Munich, 1912) — foundational, though dated
On the Vestal Virgins
Ariadne Staples, From Good Goddess to Vestal Virgins: Sex and Category in Roman Religion (Routledge, 1998)
Robin Lorsch Wildfang, Rome's Vestal Virgins (Routledge, 2006)
On the Horatii and Curiatii
Livy I.23–26 — the primary account
The story's historicity is discussed in Cornell, Beginnings, pp. 116–118, and Ogilvie, Commentary, pp. 107–116
On Just War
W.V. Harris, War and Imperialism in Republican Rome (Oxford University Press, 1979) — essential on Roman warfare and its ideology
Coleman Phillipson, The International Law and Custom of Ancient Greece and Rome, Vol. II (Macmillan, 1911) — dated but thorough on ius fetiale
On Ostia
Russell Meiggs, Roman Ostia (Oxford University Press, 2nd ed., 1973) — the standard work; dates the earliest significant archaeological evidence to the 4th century BCE
Fausto Zevi (ed.), Ostia, 2 vols. (Banco di Roma, 1996)