Why did castles change?

Answer 1

due to the advancement in technology of siege warfare

Answer 2

Person A: I am going to build a castle so I can protect myself and my people and/or belongings.
Person B: I really want some of those people and/or belongings that Person A has acquired so I am going to invent something to get me into Person A's castle.
Person A: Oh my! This castle is being destroyed by Person B, I need to build a better castle for aforementioned reasons.
Person B: Gee, Person A went and got himself a better castle. I had better get on with designing better equipment to get into the better castle.
Repeat as needed based upon architectural and technological advances.

Answer 3

After castles began being built in England and many parts of Europe, timber and earth were often employed for their construction. Unfortunately for the defendants, thse materials; even though cheap, proved to be severely weak against a well-planned attack involving fire, arrows and some siege weapons (which were available even at the turn of the millenium).

After the XII century, many nobles sought to strengthen their castles to be effective against fire. This very often involved much work and in most cases the utter reconstruction of a castle for it to be strong from its roots which was extremely useful when defending against diggers.

As it can be noted in the castle timeline, castles were oftenly enlarged because they were highly effective against foreign invaders.

When the trebuchet was invented and introduced into medieval warfare, most castles were completely re-designed in order to be once again protective because the trebuchet was a completely devastating weapon. The same held true for other common siege weapons which were often improved such as the catapult itself which often threw normous projectiles which consisted of human beings to spread disease - reason for which every part of a castle had to be accessible by the defenders to avoid a rotting body in an unreachable position.

The changes that ocurred to castles were nothing compared to what happened after the first cannon was used against a castle.

I have written a very interesting article about the changes to medieval castles after the introduction of gunppowder here.

A resource that I highly recommend is the castle timeline which emphasizes everything I have previously written enormously.

Answer 4

Because gunpowder made it easier to destroy the old castle walls and armies/nations still needed fortifications with which to protect their supply lines and territory. Read about Sebastian Vauban to see how he revolutionized castles to better defend against the cannon.

Answer 5

different architects, different styles.