They wanted to erase the old order—monarchy, nobility, and the Catholic Church—and symbolically restart history so that everything began with the Revolution itself.

Key idea in one line

By creating a new calendar, Robespierre and his supporters tried to break people’s emotional and cultural ties to “Old Regime” France and build loyalty to a brand‑new revolutionary society.

Revolution as a fresh start

  • The Revolutionaries saw 1789–1792 as the birth of a completely new era of liberty and equality, so they reset time itself to “Year I” of the French Republic.
  • If the old system was corrupt, they believed that keeping its dates, saints’ days, and royal anniversaries kept its spirit alive in people’s minds.

Attacking church and monarchy

  • The old Gregorian calendar was full of Christian festivals and saints’ days, so replacing it was part of a wider campaign to “dechristianize” France and weaken the Church’s influence.
  • Erasing traditional feast days and royal commemorations helped cut the symbolic connection to kings, nobles, and the church‑controlled past that Robespierre blamed for oppression.

Building a “republic of virtue”

  • Supporters of Robespierre talked about creating a “republic of virtue,” where citizens’ loyalties would be to the nation, reason, and revolutionary ideals—not to the king or the clergy.
  • A new, rational calendar—with new month names and a new “Year I”—was meant to constantly remind people that their true identity began with the Revolution, not with old France.

Why “every trace of France’s past”?

  • To them, “France’s past” meant injustice: absolute monarchy, rigid class privilege, and religious authority over everyday life.
  • By trying to wipe out every trace of that past—even in something as basic as how people told the date—they hoped to make a return to the old system psychologically and culturally impossible.

TL;DR: Robespierre and his supporters created a new calendar because they wanted to break with the royal and religious Old Regime and remake French society, identity, and even time itself around revolutionary ideals.