In practice, this group was very heterogeneous as it included noblemen and clericals like Henri Grégoire, François Antoine de Boissy d'Anglas, Jean-Jacques-Régis de Cambacérès, and Emmanuel Joseph Sieyès; at the same time, some of its members like Bertrand Barère, Pierre-Joseph Cambon, Lazare Carnot, and Georges Couthon joined the Montagnards in the spring of 1793.
At the time of the Montagnards' seizure of power (the days of 31 May and 2 June 1793), their centrist position at the National Convention remained ambiguous.
While the Plain deputies tried to play the role of mediators, they admitted the merits of the public safety measures voted with their support, or even their impetus, for several months; however, most of them demonstrated their hostility towards Maximilien Robespierre on 9 Thermidor, Year II, by rallying the instigators of the plot who were representatives on a mission recalled to Paris (Paul Barras, Joseph Fouché, Louis-Marie Stanislas Fréron, and Jean-Lambert Tallien).
If the name Girondins to describe the group of Jacques Pierre Brissot's followers is simply explained by their geographical origin, those of the Montagnards and the members of the Plaine continue to raise questions because several interpretations are possible.
This classification is already present in an ancient text that many revolutionaries read, the "Life of Solon" from the Parallel Lives, where Plutarch (taking up the texts of Herodotus and Aristotle) describes the political divisions in Ancient Athens in these terms: "The Hill-men favoured an extreme democracy; the Plain-men an extreme oligarchy; the Shore-men formed a third party, which preferred an intermediate and mixed form of government, was opposed to the other two, and prevented either from gaining the ascendancy.
The 1791 French legislative election resulted in a majority of around 350 moderate constitutionalists (the Plain), followed by more than 250 Feuillants (divided into Fayettists and Lametists), and a left-wing made up of around 136 Jacobin deputies, including several provincial politicians (including Armand Gensonné, Marguerite-Élie Guadet, and Pierre Victurnien Vergniaud, originally from Gironde, hence the name of the Girondins), with a small group of more advanced democrats (Lazare Carnot, Georges Couthon, and Jean-Baptiste Robert Lindet).