Complex sentence: Originally historians believed Roman villas to be primarily near urban centers and major roads, and stressed their economically autonomy since transport over land was expensive and slow, even with the improvement of Roman roads throughout Gaul (today's France).
Split into simpler sentences: Originally historians believed Roman villas to be primarily near urban centers and major roads. Historians'view of villas stressed their economically autonomy since transport over land was expensive and slow, even with the improvement of Roman roads throughout Gaul (today's France).