While there are many sources the number of people on crusade is unclear because they fluctuated regularly and many non-combatants on pilgrimage accompanied the soldiers. Historian Jonathan Riley-Smith offers a rough guide, suggesting that perhaps 43,000 people (including soldiers, armed poor, and non-combatants) were involved in the siege of Nicaea in June 1097, while as few as 15,000 may have taken part in the siege of Jerusalem in July 1099.