Complex sentence: Bohemond and Tancred marched north from Antioch to Edessa to join with Baldwin and Joscelin of Courtenay, and then marched towards Harran, about 20 kilometres away.
Split into simpler sentences: Bohemond and Tancred marched north from Antioch to Edessa to join with Baldwin and Joscelin of Courtenay. They marched marched towards Harran, about 20 kilometres away.