The Philippians - or as here and elsewhere, more authentically, Philippesians - were the recipients of one of St Paul's Epistles.
For Philippi, on the N Aegean coast, see generally OCD(4) s.v. It is best-known as the site of the battle (42 BCE) where Antony and Octavian defeated Brutus and Cassius. Philippi was the name given it by Philip II of Macedon in the 350s; in an earlier era, as a site colonized from the island of Thasos (Barrington Atlas map 51 grid D3), it had been called Krenides/Crenides ("Springs", Barrington Atlas map 51 grid C2), and now bears that name again.