Origin and early career. Antoninus was born in 86 CE at Lanuvium in Latium, into a senatorial family of Gallic origin — the Aurelii Fulvi came from Nemausus (modern Nîmes) in Narbonese Gaul and belonged to the second-or-third generation of Italian-naturalised nobility. The grandfather — T. Aurelius Fulvus, suffect consul (probably in the 70s) and ordinary consul of 89 under Domitian; the father — T. Aurelius Fulvus, consul of 89 jointly with the grandfather. Antoninus's senatorial career was standard, with no outstanding military episodes:

• Quaestorship, praetorship in the usual sequence.
• Ordinary consul of 120 under Hadrian.
• Proconsul of Asia under Hadrian (one of the most prestigious provincial positions; the exact dating is reconstructed approximately as 134–135).

Unlike the "armed" political profile standard for future emperors, Antoninus had no experience of command in significant military campaigns. This, evidently, also determined the later character of his reign as peaceful by default.

Adoption by Hadrian and the condition of the double adoption. In February 138 Hadrian, ill and urgently in need of an heir after the death of his first candidate — L. Ceionius Commodus in January 138 — adopted Antoninus. The condition of the adoption, personally dictated by Hadrian, was two-staged:

• Antoninus simultaneously adopts two boys — Marcus Annius Verus (the future Marcus Aurelius, 17 at the time) and L. Ceionius Commodus (the son of the deceased L. Ceionius, the future L. Verus, 7–8).
• This triple dynastic package — Hadrian → Antoninus → (Marcus + Verus) — was to secure the succession two generations ahead.

Hadrian died on 10 July 138, and Antoninus ascended the throne.

The cognomen "Pius." The Senate fairly quickly after Antoninus's accession bestowed on him the cognomen Pius — "the Dutiful." There are two main traditional interpretations, going back to the ancient sources (SHA Pius and Aurelius Victor):

• Antoninus insisted on the divinizatio (deification) of Hadrian against senatorial resistance (Hadrian had died unpopular; a number of senators opposed his deification). Antoninus made this point a condition of accepting power.
• Antoninus showed exemplary piety toward his elderly relatives (a stepfather? a father-in-law? the sources vary). The modern consensus (Birley and others) inclines to the first version — divinizatio of Hadrian as the formal occasion; the second is a later moralising reconstruction.

The reign 138–161: the "age of the Antonines." Long (23 years), stable, without major territorial losses and without significant civil conflicts. The military episodes of the reign — frontier operations (the construction of the Antonine Wall in Britain, c. 142; local campaigns in Dacia, Mauretania) but without Antoninus's personal participation: he, unlike Hadrian, did not leave Italy during his reign, a rarest case for a second-century Roman emperor. Foreign policy — diplomatic, defensive. Internal policy — the continuation of Hadrian's bureaucratic rationalisation without major structural reforms. The era is often characterised as the "Antonine peace" (Pax Antoniniana).

This "absence of history" in the ordinary (military-political) sense forms the basis of the later portrait of Antoninus in Marcus: the exemplar of a ruler whose measure lies in what he did not do.

Family. Wife — Annia Galeria Faustina (Faustina the Elder), died in 140/141, deified by the Senate. The Temple of Antoninus and Faustina in the Roman Forum (its surviving façade with the pronaos) was originally erected for her alone; after Antoninus's own death (161) the dedication was extended to both. Daughter — Annia Galeria Faustina the Younger, married to Marcus in 145, the mother of his children (including the future Commodus).

The adoption of Marcus and his status as heir. Having adopted Marcus in 138 by Hadrian's condition, Antoninus kept him at his side for 23 years — first as a formal heir (Caesar — a title from 139), then as a full co-ruler in the factual sense of participation in administration (although formally the tribunicia potestas and imperium came to Marcus only shortly before his accession). This long term of co-presence (from Marcus's 17th to his 40th year) makes Antoninus, in the practical sense, the principal human environment of the adult Marcus, exceeding in duration any of his teachers. Antoninus's influence on Marcus is therefore not "pedagogical" (as with Rusticus) but observational-imitative: Marcus formed himself by watching how Antoninus governed, took decisions, listened, rested.

Death and succession. Antoninus died on 7 March 161 at Lorium (his country villa near Rome), already an old man. Power passed, by his wish and by Hadrian's plan, to the joint rule of Marcus and Lucius Verus — the first joint Augustan rule in Roman history. According to the SHA Pius (12.5–7) and the SHA Marcus, the last word of the dying Antoninus — "aequanimitas" — was passed to the tribune of the praetorian guard as the watchword for the night. This death-in-aequanimitas is in the spirit of the moral aesthetic that Marcus would then codify in the Meditations.

• 01-16 (to be written) — the principal, developed portrait; the longest entry of Book I.
• Med. 6.30 — the second portrait (beyond Book I); the linkage with the imperative μὴ ἀποκαισαρωθῇς.
• 01-17 (to be written) — the thanksgiving to the gods; Antoninus is mentioned explicitly (thanks for "having received such a stepfather as Antoninus").
• Indirectly — 01-07 (through Rusticus), and also in all places where Marcus says "at the palace" or "at court": the Antonine environment is the background.

• SHA Pius (Vita Pii) — the main narrative source; unreliable in detail but giving the framework of the reign, including the famous death-word "aequanimitas" (12.5–7).
• Aurelius Victor, De Caesaribus 15 — a short imperial panegyric; the basis of Antoninus's later moralising reputation.
• Eutropius 8.8 — a short life.
• Aelius Aristides, Or. 26 "To Rome" — a panegyric contemporary with the reign; reads as the rhetorical articulation of the ideology of the Pax Antoniniana.
• Numismatics: the extensive numismatic corpus (BMCRE IV; RIC III, Antoninus Pius) — an independent source for the government programme and the legends.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000 — the fundamental reconstruction of the Antoninus–Marcus relationship; ch. 4 ("Caesar") and passim.
• A. Birley, Hadrian: The Restless Emperor, Routledge, 1997 — for the context of the adoption and Hadrian's dynastic plan.
• W. Hüttl, Antoninus Pius, 2 vols., Prague 1933–36 — the old but the most extensive monograph; still unsurpassed in the completeness of its prosopography and chronology.
• M. Hammond, The Antonine Monarchy, Rome 1959 — the institutional history of the Antonine principate.
• C. R. Whittaker, "The frontier policy of Antoninus Pius" — an article in one of the standard collections on Roman frontier policy.
• PIR² A 1513 (the exact prosopographical entry number should be verified against PIR²).