They were called letters.
If you're referring to St. Paul's letters in the New Testament, they are called epistles.
Catholic AnswerThe Catholic Epistles are those epistles of St. James, St. Jude, St. Peter, and St. John. They are so called because they are addressed to everyone, and not to a particular person or church as the epistles of St. Paul were. Two of St. John's Epistles were addressed to a particular person, but they are always grouped together and thus are label "Catholic Epistles" with his other Epistle.
St Paul is found in the bible many times He has letters from him to someone or a city (known as epistles) - such as the letter of Paul to the Corinthians, letters to Timothy 1 and 2 and others.
St. Paul wrote most of the Epistles, but there were also some written by other saints, like St. Jude, St. Peter, St. James and St. John. Check the link below for these and other references to Epistles.
Epistles - as from St. Paul, St. Peter. St. John, St. James and St. Jude.
St. Paul the Apostle is credited for writing the epistles.
Mostly those written by St. Paul (and by a few others as well).
----------------------- There is universal agreement among scholars that both Paul's epistles to the Corinthians are genuine. Paul wrote them.
St. Paul, St. Peter, St. John, St. Jude all wrote epistles. St. James also wrote an epistle but it is uncertain if he was James the greater, James the lesser or another James.
Mostly those written by St. Paul (and by a few others as well).
Thirteen New Testament epistles are attributed to Paul, beginning with Romans and continuing through Philemon.
AnswerAs far as practicable, the epistles attributed to St Paul were included in the New Testament in order of length, with the longest letter by Paul, Romans, first and the short letter to Philemon placed last. So, although Paul did not write that this would be his longest letter, its placement shows us that it is the longest epistle of Paul.