Established by Diocletian to address 3rd-century crisis
Four-ruler system: Two Augusti (Diocletian East, Maximian West) + two Caesars (Galerius & Constantius)
Dynastic strategy: Caesars married Augusti's daughters (Constantius-Theodora, Galerius-Valeria)
Regional governance: East/West division with planned abdication
Legacy: Set precedent for multiple emperors (285-476 CE)
Last non-Christian Roman emperor, attempted pagan revival
Key achievements:
357 CE: Victory over Alemanni with 13k vs 35k troops
363 CE: Failed Persian campaign died at Ctesiphon
Education: Greek philosophy enthusiast
Policy: Reduced Christian influence in government
Death: Killed in Persian retreat under mysterious circumstances
Strategic Euphrates frontier city
Cultural mix: Roman garrison + Jewish synagogue + Christian chapel
Destruction: 256 CE Sasanian siege using chemical warfare (naphtha/sulfur)
Archaeological significance: Yale holds 12k artifacts from site
Preservation: Collapsed walls created "Pompeii of the Syrian Desert"
Evolution:
250s CE: Initial raids → 286 CE treaty with Maximianus
4th CE: Franks dominated Roman military leadership
Clovis I (481-511):
486 CE: Defeated Syagrius at Soissons
506 CE: Victory over Visigoths at Vouillé
Catholic conversion (496 CE) via Remigius of Reims
Legal code: Lex Salica (510 CE) wergild system
Hunnic Empire:
439 CE: Eastern Roman treaty enforced gold tributes
451 CE: Defeat at Catalunian Plains (Roman-Visigoth alliance)
452 CE: Italian campaign halted by famine/disease
Economic strategy: Developed frontier trading posts
Death: Sudden demise post-wedding (453 CE) caused empire collapse
Regent for Theodosius II (414-450 CE)
Religious influence:
First Council of Ephesus (431 CE) affirmed Christ's divinity
Promoted Virgin Mary cult
Political marriage: To Marcian (450 CE) while maintaining virginity
Conflict: Engineered exile of sister-in-law Athenais/Eudocia
Compilation:
16 books covering 311-437 CE laws
2,500 constitutions on civil/religious law
Implementation:
Sent West with Licinia Eudoxia (437 CE)
Enforcement limited by Western instability
Limitations: Omitted key documents like Edict of Milan
Achievements:
Theodosian Walls (413 CE)
421-422 CE Persian war over Christian persecution
Controversies:
Supported Cyril against Nestorius (431 CE)
Backed "Robber Council" of Ephesus (449 CE)
Foreign policy: Paid 700lbs gold annual tribute to Huns
Impact:
25-50% Constantinople mortality
Labor shortages → Novel 122 (544 CE) wage/price caps
Symptoms: Buboes, septicemic ulcers, pneumonic hemorrhaging
Economic paradox: Survivors saw increased productivity
Recurrence: 558 CE Constantinople, 571 CE Gaul outbreaks
Key players:
Attila vs Aetius/Theodoric I
Mixed forces: Huns/Goths vs Romans/Visigoths
Significance:
Halted Hunnic expansion westward
Theodoric I killed in action
Last major Roman-Germanic alliance
Location debate: Châlons vs Troyes (Champagne)
Milestones:
330 CE: Dedication as New Rome
381 CE: Patriarchate elevated #2 after Rome
532 CE: Nika Riots → Hagia Sophia rebuild
542 CE: Plague killed 100k+
Population peak: 500k under Justinian
Defense: Theodosian Walls (5km land walls)
Roman conflicts:
260 CE: Captured Emperor Valerian
363 CE: Killed Julian at Ctesiphon
6th CE: Khusro I/II wars
Administration:
Centralized Zoroastrian state
Persecuted non-state religions
Fall: Arab conquests (651 CE) after Roman-Sasanian exhaustion