Calculator Legion

Roman Legion Strength & Structure Calculator

Military Deployment Breakdown

Total Infantry:

Total Cavalry:

Total Cohorts:

Total Centuries:

Contubernia:

Total Manpower:

*Based on the post-Marian reform structure where 1 Legion = 10 Cohorts, and 1 Cohort = 6 Centuries.

function calculateLegion() { var legions = parseFloat(document.getElementById("numLegions").value); var centSize = parseFloat(document.getElementById("centurySize").value); var equites = parseFloat(document.getElementById("equitesCount").value); if (isNaN(legions) || legions <= 0 || isNaN(centSize) || isNaN(equites)) { alert("Please enter valid positive numbers for all fields."); return; } var cohortsPerLegion = 10; var centuriesPerCohort = 6; var totalCohorts = legions * cohortsPerLegion; var totalCenturies = totalCohorts * centuriesPerCohort; var totalInfantry = totalCenturies * centSize; var totalCavalry = legions * equites; var totalManpower = totalInfantry + totalCavalry; var totalContubernia = totalInfantry / 8; document.getElementById("resInfantry").innerHTML = totalInfantry.toLocaleString(); document.getElementById("resCavalry").innerHTML = totalCavalry.toLocaleString(); document.getElementById("resCohorts").innerHTML = totalCohorts.toLocaleString(); document.getElementById("resCenturies").innerHTML = totalCenturies.toLocaleString(); document.getElementById("resContubernia").innerHTML = totalContubernia.toLocaleString(); document.getElementById("resTotal").innerHTML = totalManpower.toLocaleString(); document.getElementById("legionResult").style.display = "block"; }

Understanding the Roman Legion Composition

The Roman Legion was the backbone of the ancient world's most formidable war machine. This Legion Calculator allows you to reconstruct the scale of Roman military deployments based on historical standards established after the Marian Reforms (approx. 107 BC) and into the Early Imperial period.

The Organizational Hierarchy

• Contubernium: The smallest unit, consisting of 8 men who shared a tent and ate together.
• Century (Centuria): Commanded by a Centurion, this unit typically consisted of 80 combatants (10 contubernia). Contrary to its name, it rarely held exactly 100 men during the Imperial era.
• Cohort: Comprised of 6 centuries (480 men). The first cohort of a legion was often double-strength, containing 5 double-sized centuries.
• Legion: The primary tactical unit, usually consisting of 10 cohorts and a small contingent of 120-300 cavalrymen known as Equites.

How to Use the Calculator

To estimate the size of a Roman army, input the number of legions you wish to analyze. You can adjust the Soldiers per Century (historically between 60 and 80 depending on campaign attrition) and the number of Equites attached to each legion. The calculator will automatically break down the total number of infantry, supporting cavalry, and the sub-units required to maintain order in the ranks.

Historical Example: Caesar's Gallic Wars

During the campaigns in Gaul, Julius Caesar often commanded between 6 and 10 legions. If we calculate for 8 legions at standard strength (80 men per century):

• Legions: 8
• Total Cohorts: 80
• Total Centuries: 480
• Infantry Count: 38,400 Legionaries
• Cavalry Support: ~960 Equites

This organizational precision allowed Roman generals to manage massive bodies of men with incredible efficiency, a feat rarely matched until the modern era.