Heidegger's Bible Handbook: Colossians: Time of Writing
4. It was written at Rome in his latter bonds: sent by Tychicus, with Onesimus as his companion.
Moreover, this Epistle was written in bonds, that is, Roman bonds, as it is evident from Colossians 4:3, 18; and indeed, not the former, as many think, but the latter. For in Colossians 4:16 he makes mention of an Epistle written at Laodicea, that is, the first to Timothy, which was written after the former bonds.And it was also sent by Tychicus, with Onesimus as his companion, Colossians 4:7-9. He not a little commends this and other Epistles, because they were written in bonds. Thence it is certainly evident how much Saint Paul values the truth, since he was willing to risk and to suffer for it. In patience the sincerity of faith and love shines.