From the middle of the 5th century until 1204, Constantinople was the largest, the wealthiest, the most sophisticated, the most important city in Europe. Then the 4th Crusade, which had intended to go retake Jerusalem, went to the center of Eastern Christianity and besieged it, sacked it, crippled it, and destroyed -- for at least 800 years -- the relations between the Roman Christians and the Byzantine Christians.  None of this makes any sense, except that money was involved and people behaved badly. Michelle explains how Western scholarship has dealt with this major crime (it wasn't until the 1950's that it was described as a crime), and Anne explains the money.  Follow the money.