After the defeat of Caliph al-Amins' army at the Battle of Rayy and the death of his commander Ali ibn Isa ibn Mahan, the armies of al-Amin were in retreat moving west from Iran to Iraq back to their base camp at Baghdad. Future Caliph Al-Ma'mun's general Tahir ibn Husayn, the victor of Battle of Rayy decided to chase the retreating army. However, reinforcements from Baghdad arrived under the able leadership of Abd al-Rahman ibn Jabala. Abd al-Rahman decided to fortify himself behind the walls and gates of Hamadan. But when Tahir ibn Husayn came closer to the city, Abd al-Rahman decided to come out and meet this threat head on. Twice Abd al-Rahman was driven back into the city. Tahir ibn Husayn began a blockade of the city and Abd al-Rahman’s forces began to shower arrows and throw stones