the hakkas are northerners who migrated to the south, in btw song to ming dynasty. when they began to settle in the south, they had problems in assimilating into the new environment, particularly language problems cos ppl in the south oredi formulated their own dialects, and oso had fear that the locals will bully them. so they built rounded fortress that can house over 1 hundred families and lived separate from the local population. they are the last batch of major migration among the chinese in the history of china, and bcos of their conservative attitude they maintained cultures that was passed down since ming dynasty. in some places they are the symbols of 'ancient chinese'(actually meaning middle ages chinese, some 600-700yrs back). they oso maintain the language of ming dynasty people and a lot of their pronounciation are very close to modern mandarin(modern mandarin evolved from ming/qing dynasty common tongue). they are, however, probably the youngest of the 7 major dialects in china, and are very different from ancient chinese.