The Medieval Ages ended in the 15th century[1], and slavery didn't really start to end until the 19th century [1].
[1] https://en.wikipedia.org/wiki/Middle_Ages [2] https://en.wikipedia.org/wiki/Abolitionism
[1] https://en.wikipedia.org/wiki/Middle_Ages [2] https://en.wikipedia.org/wiki/Abolitionism
https://en.m.wikipedia.org/wiki/Slavery_in_ancient_Rome https://en.m.wikipedia.org/wiki/Slavery_in_medieval_Europe
A big hindrance to seeing continuity is that popular knowledge of "romanness" is so focused on the late republican/early imperial era and there is surely not much visibly continuity between early medieval and a snapshot of the Roman state outdated by several hundred years.
[1] https://en.m.wikipedia.org/wiki/Slavery_in_the_21st_century