Bastides have many features in common, but even so it is difficult for historians, architects and town planners to agree on a precise definition, as each Bastide, although planned and organised along similar lines, also has a unique form and origin.
The terme " bastide " comes from the Occitan " bastida ", which means a building. 

The construction of the Bastides represented a wave of development, which began in Southern France in 1229 and ended with the building of Labastide d'Anjou in 1373. 

In practice, each one might look slightly different or have a different history, but we can say that a Bastide is, basically, the result of a medieval urban planning policy, where a public authority created an unconfined urban area in the tradition of the villages surrounding castles and religious houses. The reasons for building a Bastide depended on the founding authority: they might be economic, administrative, political or military. But in most cases, it was a question of attracting a population (by offering privileges, or more rarely, by force) to settle in a defined area, where they would then be subject to taxation. The area had a simple geometric shape, the square, which made drawing up the town plan much simpler and meant that the ground could be divided up fairly between the new inhabitants. This explains the checkerboard pattern of many Bastides, which has hardly been touched by modern roads: two main thoroughfares( cart tracks) which cross at right angles in the centre of the village and off which run the alleys which give access to the dwellings (known as andrones or carrérots).
But the main innovation was the large public square, which occupied a central position, both literally and figuratively, in the organisation of these new towns.