Findings: Hungry army sacked empire

While all armies march on their stomachs, the fourth crusade was led by its belly to one of the most shameful episodes in medieval warfare.

The chain of events that prompted a Christian army to abandon plans to attack Muslim Egypt and instead sack Constantinople, the Christian capital of the Byzantine empire, has long puzzled historians.

New analysis of 13th-century treaties and eyewitness testimonies by Thomas Madden, professor of history at Saint Louis University in the US, suggests that scholars have overlooked the central role of food and the provisioning of the ill-fated expedition.

His findings were outlined at the International Congress on Medieval Studies.

The fourth crusade was launched in 1202 with the intention of invading Egypt.

Professor Madden said that a crucial treaty between the crusaders and the Venetians contracted to transport the army had been misunderstood by scholars.

While most historians have accepted that this involved provisioning the first year of the crusade, he argued that it involved supplying food for the troops only while at sea.

But the expedition delayed its departure for three months while gathering its strength and by the time it was ready to set off, most of its provisions had been consumed.

Faced with the prospect of starvation, the lure of being fed and paid by a challenger to the Byzantine throne was too powerful for the desperate crusaders to resist.

The mission was diverted to Greece. Things turned sour when the new emperor paid only half of what he owed the army. He was then overthrown in a palace coup and his successor ordered the crusaders to leave the empire.

By this time, the crusaders were again short of food and money and their leaders felt they had little option but to attack.

The assault saw the slaughter of civilians, the looting of churches and the raping of nuns and was later followed by a catastrophic fire.

It would take centuries - and a new Muslim government - to restore the glory Constantinople lost to the hungry crusaders.