A thank-you letter written from custody to the congregation Paul seems to have liked best, containing the oldest surviving Christian hymn and no idea where it was written from.
What the book is
Philippians is a letter of thanks and encouragement to the church at Philippi, written by Paul while in custody. It reports on his situation, urges unity, warns against teachers pressing circumcision, names two women in a dispute, and thanks the congregation for money sent.
Its tone is unlike anything else in the corpus. Where Galatians is furious and 2 Corinthians is wounded, Philippians is affectionate, and it is affectionate from prison.
How it is put together
The letter moves through news, exhortation, warning, thanks. A sharp break at chapter 3 — from farewell language into sudden polemic — has led some to read the letter as a composite of two or three shorter notes later joined. Others treat the shift as Paul’s own change of subject, which he does elsewhere.
Chapter 2 contains the passage usually called the Christ hymn: a compact, rhythmic account of descent, humiliation and exaltation. Its vocabulary and structure differ from Paul’s surrounding prose, and the common view is that he is quoting something already in circulation. If that is right, the hymn is older than the letter, which makes it the earliest datable Christian composition of any kind that we have.
The dating question
Paul is in custody, but he does not say where, and the letter is dated differently depending on the answer.
Rome, in the early sixties CE, is the traditional location, supported by the reference to the praetorium and to the household of Caesar — though both terms were used in provincial capitals too. Ephesus, in the mid-fifties, is argued from the number of journeys the letter implies between Paul and Philippi, which is easier over a short distance than across the Mediterranean; against it, no imprisonment at Ephesus is directly attested. Caesarea is a third proposal with fewer defenders.
The uncertainty is about a decade, and it does not much affect how the letter reads. It is a good example of a case where the honest answer is a range rather than a date.
Where the external record touches it
Philippi is well excavated. It was refounded as a Roman colony after the battle of Actium in 31 BCE and settled with veterans, and the epigraphic record confirms a heavily Latinised civic culture with Roman institutions and Roman citizens — which is the background to the letter’s language about citizenship in chapter 3 and to the pride in Roman status that Acts 16 attributes to the city.
The forum, the theatre and a stretch of the Via Egnatia are visible on the site. What none of this does is attest the letter or the events in it. It attests the setting, which is a real but limited thing, and the distinction is worth keeping.
The manuscript evidence is the usual Pauline situation: P46, around 200 CE, contains the letter.
Related: the overview of Acts, whose chapter 16 narrates the founding of the church at Philippi, and Colossians.