Gaining recognition for his innumerable works on the history of Brittany, he enlivened research in many areas and inspired many historians by his influence and example.
He was the director of the historic review Revue de Bretagne et Vendée (published from 1867 to 1900) that he founded aged 25.
In particular he led the investigation into events at Camp Conlie where 50,000 Breton soldiers were held and supposedly mistreated in 1871.
His report was overwhelmingly critical of the French army, which demonstrated a total lack of organization.
In the years after the Franco-Prussian War he re-formed the Association bretonne which had been dissolved as suspect by the government of Napoléon III.