This is the so called Temple of Diana at Nimes:
But we do have an in depth discussion of a late Gallo-Roman library courtesy of Sidonius Apollinaris, an interesting chap I encountered in my research of the era. Sidonius lived from about 430 to 489, a time in which he witnessed and chronicled the final days of the Western Empire. Being at various times a Roman official, a poet, a prisoner and a bishop he leaves us an extensive collection of letters.
In one notable letter of about 461 AD he describes the library at a still sumptuous Gallo-Roman villa:
".....books in abundance ready to your hand; you might have imagined yourself among the shelves of some grammarian, or the tiers of the Athenaeum, or a bookseller's towering cases.2 They were so arranged that the devotional works were near the ladies' seats; where the master sat were those |51 ennobled by the great style of Roman eloquence. The arrangement had this defect, that it separated certain books by certain authors in manner as near to each other as in matter they are far apart. Thus Augustine writes like Varro, and Horace like Prudentius; but you had to consult them on different sides of the room.  Turranius Rufinus' interpretation of Adamantius Origen1 was eagerly examined by the readers of theology among us; according to our several points of view, we had different reasons to give for the censure of this Father by certain of the clergy as too trenchant a controversialist and best avoided by the prudent; but the translation is so literal and yet renders the spirit of the work so well, that neither Apuleius' version of Plato's Phaedo, nor Cicero's of the Ctesiphon of Demosthenes is more admirably adapted to the use and rule of our Latin tongue."
Sidonius also goes on at length about the fine baths, the elegant banquets and the urbane, hospitable hosts at the country villas of that time. To really appreciate the "soft landing" of Roman Gaul contrast this idyllic scene with what was then happening in post Roman Britain. The province had by then been in barbarian hands for half a century, and archaeologists find that the dead were lying unburied in the streets of former Roman towns.
Why things survive: The "Temple of Diana" was long in use as a church. The writings of Sidonius, while of mediocre literary quality, probably were preserved because he was an early bishop. He in fact became a saint, with his own Feast Day on August 21st.
Practical tips for a visit. The Jardin de la Fontaine is off the beaten track for tourists. If you are in doubt as to its location steer for this:
Temple of Diana photo credit to Daniel Villafruela