March Content Update: Addendum - The Sizes of Some Historical Armies (Patreon)

A Note on Sources: A lot of the armies on this list have multiple sizes attested to them in various sources. For the purpose of this reference, I'll be leaning towards lower estimates. Ancient sources tend to exaggerate the size of armies for various reasons. Likewise, historians writing from one side of a conflict tend to exaggerate the size of the enemy's forces to make their own side's victory more impressive or defeat more excusable. Naturally, ancient sources writing about the enemy (like Herodotus writing about the Persian Army at Thermopylae) exaggerate doubly.

ANCIENT

Egyptian Army - Megiddo - 1457 BC

Size: Approx 11 000

Notes: First reliably recorded major battle. Major-effort short range expeditionary force by a major power.

Persian Army - Thermopylae - 480 BC

Size: Approx 200 000

Notes: Maximum effort short ranged expeditionary force by a major power. Supplied by sea, but still exceeded logistical capabilities and suffered severe losses from starvation and lack of supply.

Roman Army - Cannae - 216 BC

Size: 86 400

Notes: Maximum effort force raised by mass conscription from a heavily militarised city-state and its allies (comprising of most of Italy). Operating on home territory.

Cao-Wei Army - Chibi - 208 

Size: 220 000

Notes: Maximum effort short range expeditionary force by a major power (which controlled the most populated and politically unified parts of China). Supplied by, and moved along major waterways.

MEDIEVAL

German-Imperial Army - Lechfeld - 955 

Size: Approx 10 000

Notes: Maximum effort defensive force drawn from multiple component states of the Holy Roman Empire, reinforced by the city garrison of Augsburg. Operating on home territory.

Crusader Army - Jerusalem - 1099 

Size: Approx 12 000

Notes: Major effort long range expeditionary force including major portions of the military aristocracy of Western Europe. Only about 1/4th of force at start of First Crusade due to attrition and lack of supply.

English Garrison - Chateau Gaillard - 1203 

Size: Approx 100

Notes: Typical size of garrison for a major European fortification of the High Middle Ages.

Anglo-Imperial Army - Bouvines - 1214 

Size: Approx 8 000

Notes: Major effort short ranged expeditionary force from two major European powers (England and the HRE). Operating in relatively wealthy and populated region.

Polish-Lithuanian Army - Tannenberg-Grunwald - 1410 

Size: Approx 25 000

Notes: Maximum effort defensive army of two major European powers in personal union. Operating on home territory.

EARLY MODERN

Ottoman Army - Siege of Constantinople - 1453 

Size: Approx 60 000

Notes: Maximum effort by major early-modern power. Force contains sizeable number of full-time professionals, operating very close to home territory.

Spanish Expeditionary Force - Cortes Expedition - 1519 

Size: 630

Notes: Long range colonial expedition. Includes large number of non-combatants. Conquest of Aztec empire only made possible by superiority of equipment, and massive reinforcement by subsequent Spanish expeditions and local allies.

Japanese Invasion Force - Imjin War - 1592 

Size: 162 000

Notes: Maximum effort short range expeditionary force by heavily militarised early-modern power. Number includes support personnel and non-combatants. Force divided into 7 corps, none exceeding 30 000.

Spanish Army of Flanders - Siege of Ostend - 1601 

Size: 80 000 (total)

Notes: Maximum effort force drawn from throughout the territories and allies of a major European power. Rotated in and out of front lines to maintain continuous siege due to logistical constraints. Still loses more than 1/2 of its number to attrition in course of three-year siege.

French Army - Rocroi - 1643 

Size: 23 000

Notes: Typical size of major field army of the period. Operating on home territory.

Coalition Army - Blenheim - 1704 

Size: 52 000

Notes: Major effort force drawn from coalition of three major European powers (Britain, the Netherlands, and the HRE). Comprised of two field armies (Anglo-Dutch and Imperial) which marched separately and united to fight major action.

Franco-Spanish Army - Siege of Gibraltar - 1779

Size: 65 000

Notes: Major effort by two major European powers operating on home or allied territory. Ironically the largest battle of the American War of Independence, despite occurring in Europe.

Franco-American Army - Yorktown - 1781

Size: 19 800

Notes: Coalition force divided almost evenly in number between maximum effort of a minor power fighting on home territory and major effort of long range expeditionary force by major European power.

LATE MODERN

Coalition Army - Leipzig - 1813

Size: 365 000

Notes: Coalition force made up of maximum effort of just about every single major power in Continental Europe (except Napoleonic France, obviously). Made up of 33(!!) individual Army Corps, which marched separately and concentrated into a single force for battle.

East India Company Army - Chillianwala - 1849

Size: 15 000

Notes: Maximum effort short range expeditionary force made up primarily of locally recruited troops of (extremely large) private corporation, bolstered by units of the British Army, seconded to Company control.

French Army - Puebla - 1862

Size: 5 730

Notes: Major effort long range expeditionary force by major European power.

US Army of the Potomac - Antietam - 1862

Size: 87 164

Notes: Major effort by secondary power raised through mass conscription, supplied by extensive railroad networks, and fighting on home territory. Primary field army out of several fielded at the same time.

French Army of the Rhine - Siege of Metz - 1871

Size: 154 481

Notes: Major effort by major power raised through mass conscription, supplied by extensive railroad networks, and fighting on home territory. One field army out of several fielded at the same time.

Ethiopian Army - Adwa - 1896

Size: 73 000

Notes: Maximum effort by pre-industrial secondary power raised through local levies and supplied primarily through traditional means, fighting on home territory. Multiple forces united for single battle.

Anglo-Egyptian Army - Omdurman - 1898

Size: 25 800

Notes: Major effort long-range expeditionary force by major power and its protectorate. Spent two years building railroad and river infrastructure needed to maintain supply needed for a major engagement.

British-Imperial Army - Southern Palestine Campaign - 1917

Size: 18 000

Notes: Minor effort long-range expeditionary force by major power and several of its dominions, drawn from mass-conscript armies raised for First World War. Lack of plentiful railroad infrastructure or supplies of fresh water placed heavy logistical constraints on force.

Allied Army - Vittorio Veneto - 1918

Size: 1 486 200

Notes: Vast majority of force consisted of maximum effort by secondary power (Italy) raised by mass conscription and supplied by railroad. Deployed along front approximately 200 km long in home territory.

NRA Central Army - Shanghai - 1937

Size: 700 000

Notes: Maximum effort force by secondary power (Nationalist China) fighting in single heavily urbanised area on home territory.

Soviet Army - Rzhev - 1942

Size: 3 680 300

Notes: Major effort force by major power (Soviet Union) fighting on home territory, raised by mass conscription and supplied by railroad. Deployed along front approximately 1000 km long.

Burma Area Army - Burma Campaign - 1944

Size: Approx 90 000

Notes: Long range expeditionary force primarily made up of major effort of major power (Imperial Japan), bolstered by collaborator units (Indian National Army). Intended to rely on captured Allied supplies to survive, and was annihilated by attrition when expected victories failed to materialise.