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From Forum to Castrum: The Birth of Fortified Towns

From Forum to Castrum: The Birth of Fortified Towns

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4th Century: The Christian Empire · FROM 50 BC TO THE FALL OF ROME

In the 4th century, the Gallo-Roman city changed radically. Constant insecurity turned open towns into closed fortresses.

🏗️ Urban contraction

Large cities of 100 hectares could no longer be defended.

  • Withdrawal: inhabitants abandoned outlying districts to regroup inside an area ten times smaller (often under 10 hectares).
  • The castrum: a thick enclosure was built — the castrum. In Bordeaux, Périgueux, or Amiens, you can still trace these ancient walls beneath medieval streets.

🧱 Recycling monuments

To build quickly, people no longer went to quarries.

  • Spolia: theatres, temples, and arenas outside the walls were dismantled. Foundations of 4th-century ramparts often contain broken statues and columns.
  • Symbol: it is the material end of the classical world — stone once used for pleasure (theatre) now served survival (walls).

Walls of Senlis The Gallo-Roman walls of Senlis, evidence of urban fortification.

🛡️ The ancestor of the castle

These fortified towns became the basis of medieval defensive systems.

  • Towers and gates: military architecture evolved with projecting towers to watch over the walls.
  • Power: whoever controlled the rampart (often the bishop or a military leader) held real power over the population.

🧠 Key takeaways

  • Contraction: cities became small and dense.
  • Recycling: Roman monuments were reused to build ramparts.
  • Castrum: the model of the walled medieval town was born.

📸 Image credits