Complex sentence: The Romans not only trained them to attack, but also bred their attack dogs for ferocity, the effect of this was documented by Roman naturalist and writer Pliny the Elder, who wrote that the animals would not back down, even when confronted by swords.
Split into simpler sentences: The Romans not only trained them to attack, but also bred their attack dogs for ferocity. The effect of this was documented by Roman naturalist and writer Pliny the Elder, who wrote that the animals would not back down, even when confronted by swords.