(written from a Production point of view)
Referred to in a deleted scene from ENT: "Fight or Flight" and in the revised final draft of that episode's script, Lavinius was a planet. In 2151, Ensign Travis Mayweather told Captain Jonathan Archer that the freighter Horizon once made a two-light-year journey from Lavinius to Bylaran Prime. The trip took the freighter approximately nine months.
As evidenced by the final draft script of "Fight or Flight" (dated 1 May 2001), the reference to Lavinius was at one point intended to be a reference to Andoria instead. The planet's name change to "Lavinius" was made by or on 27 June 2001, when the revised final draft of the script was issued.
The scene mentioning Lavinius is available as a deleted scene on the ENT Season 1 DVD. The planet's name was spelled "Lavinius" in the revised final draft of the teleplay and "Livinius" in the subtitles on the DVD release.