There is no definite answer as it depends on the conditions; for example:
The King/Queen/lord/baron wants to save his/her citizens, so they build castles to protect them.they were also built like motte and baileys only to protect royalty
castles was built anywhere the commander wanted his men to build him the castles.
Castles were also built for its defentive features and to help protect the people if the king/queen/lord/barcon wants to.
'Proper' castles, as in those built for military purposes, were usually built to guard strategic areas and provide a base of operations for forays into enemy territory. Other considerations were also important, such as making use of natural defenses such as hills or cliffs (it is not a coincidence that so many castles were found on hills or cliffs, as the high ground and difficult terrain was crucial to their defence), and logistical concerns played a large part - a castle that could be easily resupplied was a difficult castle to siege.
The best examples of strategic castle placements are probably those built by Edward I during his campaigns in Wales. Beaumaris, Conway, Harlech and Caernarfon Castles were notable parts of his 'Iron Ring' designed to secure his hold on Wales. They were placed at roughly equidistant points around the Welsh coast, particularly in the north, to contain and control the uprising Welsh people. Their locations near the coast allowed them to be resupplied by sea, virtually eliminating the risk of a successful siege attempt, while castles such as Conway and Harlech made good use of natural fortifications to make them more difficult to assault. Caernarfon in particular guarded a strategic area, built as it was to guard the Menai Strait.
The psychological impact of castles such as these was not to be underestimated either. Edward I placed several castles as a means to increase pro-English feelings in particular areas. Caernarfon, its formidable walls being brilliant-white at the time of their construction, stood as a symbol of English might in the region.
As another important point, many castles - including many of the castles in the Iron Ring - were built on the sites of previous castles, somewhat reducing the amount of work needed to be done.
Over time, as the military effectiveness of castles was eroded by new weapons such as the cannon, castles were built less for practical reasons and more for vanity and status, by nobles with money wishing to have palatial residences that looked like castles, but had none of their defensive abilities.
They were built, to be better than the other castles and the truth is that they are the best protected castles that were built. :)
Norman castles were built on mounds.
Castles were built out of stones or bricks.
the first castles were built in aroundAD900.
The earliest and the proper castles were built in 1066. These castles were built in England after the Norman Conquest. They were introduced by William the Conqueror.
Stone castles were built because they could not burn down as ealsily as wood castles can.
he built woodern castles He built these castles in England for better defence.
The first castles ever built were in sri lanka.
over 1000 castles where built!!
in 1400 castles stopped being built
they built round keep castles because they did
Medieval castles were built out of stone, mortar, and wood.
Stone castles, Concentric castles, Motte and Bailey Castles
William the Conquerer built the shell keep castles
Medieval castles were built in 1067.(in the time of the Normans)
Most castles were built in the 16 hundreds.
Castles were built only for kings because they were used to keep the kings built.
Castles were built in lots of different countries. Initially they were built in England by the Normans.
king william built Motte and Bailey castles and also stone keep castles
motte and bailey castles
Castles were built as protection from enemies.
Meiveal castles were built for protection in wars to protect the people of the town e.g. Caernarfon Castle built in 1218. However castles built now have much less meaning and thought and are built purely for decerational matters
William the Conqueror built the first wooden ones but kings after him also built their own castles.
Square keep castles were mainly built far from villages