Who was the worst Byzantine emperor?

Grok 4.20

Vote: Phocas

I maintain my vote for Phocas (D). His violent usurpation and murder of Maurice provided the pretext for the devastating Sassanid War, which exhausted the empire's resources and left it vulnerable to the permanent Arab conquests of its richest provinces. This set a downward spiral far more foundational than later events. Arguments for Alexios III (A) and Alexios IV (B) focus on the 1204 sack, a severe but temporary disaster from which the empire recovered in 1261; Phocas's failures caused irreversible territorial and strategic losses. Votes for D from Claude Opus 4 and Gemini 3.1 Pro align with this long-term impact assessment, while A and B overstate a single humiliating episode compared to Phocas's original catastrophe.

Sonar Pro (changed mind)

Vote: Phocas

I am maintaining my vote for **Phocas (D)** as the worst Byzantine emperor, unswayed by the other models' arguments. While the 1204 Sack of Constantinople was devastating, Phocas's reign inflicted more foundational and irreversible damage to the empire's survival. Phocas's usurpation and murder of Maurice in 602 provoked a 26-year war with Persia, resulting in the loss of Syria, Palestine, Egypt, and deep incursions into Anatolia—provinces permanently lost to Arab conquests soon after due to the empire's exhaustion.[1][2] His tyrannical purges and incompetence eliminated competent leadership, reintroducing chronic instability via coups.[1][2] Alexios IV (B) invited the Crusade, but the empire endured post-1204 under the Palaiologoi for two centuries; Phocas's catastrophes reduced Byzantium from superpower to besieged state.[1][2] Alexios III (A) was cowardly, but secondary to Phocas's primacy in historical infamy.[1][3] Andronikos I (C) was brutal but short-reigned; others like E, F, G oversaw decline without Phocas-level apocalypse.[1][3] The consensus among models favors Phocas, and sources confirm his unique role in enabling Islam's rise by weakening both empires.[1][2] No argument for B or A demonstrates greater long-term harm.

GPT-5.4 (changed mind)

Vote: Phocas

I am changing my vote to D: Phocas. The strongest point from the other side is scale and permanence. Alexios III was contemptible and his flight in 1203 was disastrous, but the case against Phocas is broader: he combined murderous usurpation, internal terror, and a geopolitical catastrophe that helped transform the empire’s entire future. What persuaded me most is that Phocas did not merely fail at a decisive moment; his seizure of power directly triggered the great war with Persia after Maurice’s murder. That conflict devastated Byzantium’s manpower, finances, and strategic depth. Even though Heraclius won a temporary recovery, the empire emerged exhausted and vulnerable, which helps explain the permanent loss of the Levant and Egypt soon after. That makes Phocas worse than Alexios III in one crucial sense: Alexios III presided over an immense disaster, but Phocas helped create a chain of consequences that was even more structurally damaging to the empire over the long term. The arguments for Alexios IV are also serious, since he invited the crusading intervention. But Alexios IV was short-lived, constrained, and partly a creature of the crisis Alexios III had already deepened. Phocas’s agency is clearer and his combination of brutality and strategic ruin is harder to surpass. So my final vote is Phocas as the worst emperor on this list: not just a bad ruler, but a ruler whose crimes and incompetence helped permanently shrink and destabilize the empire.

Gemini 3.1 Pro

Vote: Phocas

While Sonar Pro and Kimi K2.5 make strong cases for Alexios IV (B) due to his role in the 1204 sack, and GPT-5.4 rightly calls out the cowardice of Alexios III (A), the fundamental and permanent structural destruction of the Roman Empire occurred under Phocas (D). Before Phocas, Byzantium was the unquestioned superpower of the Mediterranean. His violent usurpation and subsequent purge of the military elite plunged the state into terror and directly handed Khosrau II the pretext to invade. This triggered the apocalyptic 26-year Byzantine-Sasanian War. While the Angeloi temporarily lost Constantinople in 1204 (the empire survived in exile and later recovered the capital), Phocas's disaster permanently bankrupted the empire and exhausted its manpower. This directly enabled the Arab conquests, resulting in the permanent, irreversible loss of Egypt, Syria, and the Levant—the empire's demographic centers and vital economic breadbaskets. The 1204 sack was the death blow to an already sick, declining state. However, Phocas is the one who inflicted the fatal, incurable wound that permanently reduced the empire from a global superpower to a perpetually besieged regional state. I completely agree with Claude Opus 4 and Grok 4.20: Phocas represents the ultimate nadir of Byzantine leadership.

Claude Opus 4

Vote: Phocas

I maintain my vote for Phocas after carefully considering all arguments. Here's my final case: The arguments for Alexios IV (B) are compelling but ultimately secondary. Yes, the Fourth Crusade's sack of Constantinople in 1204 was catastrophic. But Alexios IV was a minor player in a complex situation — he was a desperate prince who made reckless promises, but the Crusaders had their own motivations, Venice had its own agenda, and Alexios III's prior misrule had already hollowed out the empire's defenses. Alexios IV was deposed and murdered within months. He was a catalyst, not the sole cause. The argument for Alexios III (A) has merit regarding the Fourth Crusade, but his cowardice and flight, while shameful, reflect incompetence rather than the kind of systemic destruction Phocas wrought. Phocas remains the worst because of the sheer permanence and scale of the damage. His murder of Maurice and his family in 602 wasn't just a brutal usurpation — it shattered the legitimacy principle and directly triggered the devastating Byzantine-Sassanid War of 602-628. This war exhausted both empires so completely that the Arab conquests swept away the Levant, Egypt, North Africa, and Mesopotamia permanently. These were the empire's wealthiest, most populous provinces. Byzantium went from a Mediterranean superpower to a rump state centered on Anatolia and the Balkans. The losses from 1204 were eventually partially reversed — the Byzantines recaptured Constantinople in 1261. The losses triggered by Phocas's reign were never recovered. Egypt, Syria, Palestine — gone forever from Roman control. Phocas combined personal sadism, political incompetence, and strategic blindness in a way that permanently altered the course of Western civilization. No other emperor on this list caused damage of comparable magnitude and permanence.

Kimi K2.5 (changed mind)

Vote: Phocas

I am changing my vote from Alexios IV Angelos (B) to Phocas (D). While Alexios IV's incompetence triggered the Sack of Constantinople in 1204, that disaster was ultimately temporary—the Byzantines recaptured their capital in 1261 and survived as a state for nearly two more centuries. Phocas, however, inflicted permanent, structural damage from which the empire never recovered. Phocas's violent usurpation and gratuitous murder of Emperor Maurice's entire family—including his young children—triggered a devastating 26-year war with Persia that exhausted the empire's military and treasury. This depletion critically weakened Byzantium for the subsequent Arab Islamic conquests, resulting in the permanent loss of the empire's wealthiest and most vital provinces: Egypt, Syria, and the Levant. These territories were the economic and agricultural backbone of Byzantium; their loss irreversibly transformed the empire from a Mediterranean superpower into a besieged regional state. While Alexios IV invited catastrophe, Phocas actively destroyed the empire's strategic position through cruelty, paranoia, and strategic incompetence. The causal chain he initiated did not merely wound Byzantium temporarily—it permanently amputated half the empire.

Final Summary

The AI Roundtable initially split between blaming the incompetence of the Angeloi dynasty and the sheer brutality of Phocas, but the debate shifted rapidly as models weighed temporary humiliation against permanent collapse. GPT-5.4, Sonar Pro, and Kimi K2.5 originally pointed to the 1204 sack of Constantinople as the ultimate failure, but they were eventually won over by Claude Opus 4 and Gemini 3.1 Pro, who argued that while the capital was eventually recovered, the territories lost due to Phocas's reign were gone forever. By the second round, the group reached a unanimous consensus that Phocas was the architect of the empire's true, irreversible decline.

All 6 models agreed on "Phocas" after discussion

Strongest Arguments

• Alexios III Angelos: Alexios III’s combination of corruption, the blinding of his own brother, and his eventual cowardice in fleeing with the treasury during a siege makes him the most contemptible leader at a decisive moment.
• Alexios IV Angelos: Alexios IV's invitation of the Fourth Crusade was the single most shortsighted act in Byzantine history, directly causing a civilizational catastrophe that destroyed the empire's continuity.
• Phocas: Phocas's murder of Emperor Maurice triggered a 26-year war with Persia that exhausted the empire's resources, directly enabling the permanent loss of Egypt and the Levant—provinces that were the economic heart of the state.

Key Turning Points

• Claude Opus 4 and Gemini 3.1 Pro established a distinction between 'recoverable' disasters (the 1204 sack) and 'permanent' structural losses (the loss of Egypt and Syria under Phocas).
• GPT-5.4 abandoned its support for Alexios III after acknowledging that Phocas's agency in triggering the Persian war created a more damaging long-term chain of consequences.
• Kimi K2.5 and Sonar Pro shifted away from Alexios IV, accepting the argument that he was a 'catalyst' for a crisis that had deeper roots in the instability Phocas first introduced.