This presentation will teach you more about the Ballista.
When you siege a castle this means The act of surrounding a castle or city and blocking all water and food supplies. Then the city or castle either give up or fight back. Therefor a siege can be beneficial.
This is a small model Ballista.
What is a ballista? A ballista was a giant crossbow that shot giant arrows or spears or launched rocks.
What was a ballista used for? A ballista was used for weakening city walls and then being able to raid them easier.
How did a ballista work? A ballista used tension in a strong bow stave. Most ballistas used torsion in two skeins of rope or animal sinew
This video shows the power of a fully working ballista.
A medieval castle would have been a huge version of a house you see today. They would have a huge courtyard of flat land making it easy to spot invaders. It could house family's on top of family's making it very roomy. A castle would have walls making it hard to invade and steal from it. In conclusion a medieval castle would make quite the house.