Lots of information on the different types of trebuchets.
Medieval Warfare by Use the keyword Knights OR Military history OR Middle Ages to search using Fast Find on the library catalogue. There are a variety of resources availalbe on this topic. These books are only a small selection.
Warfare in the Middle Ages by 
Soldier : a visual history of the fighting man by The following title is a digital book. Click on the cover below to take you to the eBook and the information it contains including information about warfare. If you click on it out of school hours you will need a password from the school library.
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