The ancient Romans tried to define what makes one civilized using themselves as the role model.
Julius Caesar and other Romans saw those Gauls as civilized who had cut hair, shaved beard and followed Roman mannerism.
However, those tribes such as the Nervii of present day Belgium were seen as untouched by civilization. Interestingly, the Nervii gave an extremely tough fight in the Gallic Wars.
In the war of conquest against the Gauls, the Romans under the leadership of Julius Caesar went all out in their efforts.
The origins of this conflict lay around 350 years prior to this final war in the Battle of the Allia, when the Gauls sacked Rome.
During the war with Rome, the Gauls put up incredible resistance until the end. The last stand took place at Alesia.
As the ancient Roman empire moved into the late antiquity, the empire began to feel the impact of the significant Christian minority inside the empire. At the same time, it appears that the early Christian scholars picked up the dominant philosophies of the time and began to be influenced by it.
Also, the emperor and the imperial government began to have more of a presence in the various cities of the empire. So most of the upper classes began to rely of the emperor’s good graces to maintain their class status. Many of the old ways and customs began to transform in accordance with the times. As the emperor Constantine established the Christian religion as the official religion, this process accelerated.
As one reads about the daily lives of ancient Romans, one runs across the two major schools of philosophy: stoicism and epicureanism. These schools, along with other smaller schools such as cynicism, contended for the minds of the citizens of the Roman Empire. However, these schools were not proselytizing by nature. Citizens were attracted to them per individual tastes and mindsets.
Alongside this, one observes that the intellectuals among the ancient Romans, such as Cicero, were not great believers in the pagan gods of the day. The attitude to religion overall was that of customary common practice, rather than having a prepackaged set of beliefs which had to be digested by each follower. It appears that it was mainly near the Eastern borders of the empire that people were more prone to pay obeisance to their potentates and thus, had a more servile attitude towards their gods.
We read about patrimony, evergetism, and other interesting practices of the ancient Romans.
Also, it is interesting that the Romans regarded the gods as merely one step above the humans, who were in turn seen as one step above animals. So, the cultured Romans did not believe in a servile relationship with gods unlike the peoples of Eastern regions of those times.
Slavery was seen as quite natural and part of daily life, although some of the followers of stoicism later on did have reservations with this practice.
All these and other fascinating details can be gleaned from the fascinating History Of Private Life. This is a multi-volume work encompassing periods all the way from ancient Rome to the modern day.