when in Rome, do as the Romans do

The story

1. Medieval Latin · derived fromsi fueris Rōmae, Rōmānō vīvitō mōre; si fueris alibī, vīvitō sīcut ibī“if you should be in Rome, live in the Roman manner; if you should be elsewhere, live as they do there”
2. English todaywhen in Rome, do as the Romans do

The first attestation is Medieval Latin si fueris Rōmae, Rōmānō vīvitō mōre; si fueris alibī, vīvitō sīcut ibī (“if you should be in Rome, live in the Roman manner; if you should be elsewhere, live as they do there”), which is attributed to St Ambrose (c. 339–397). Robert Burton in his Anatomy of Melancholy (1621) uses the phrase “When they are at Rome, they doe there as they ſee done.”