Breaking up kriah among several readers

In the time of Chazzal, every one who got an Aliyoh would read it himself (so the Parsha was read by 7 ba'alei Kri'oh). Later, since not all people knew the ta'amim - the chazzen used to read the Parsha. Even later, when the Chazzens also did not know how to read properly came the minhag that there is a Ba'al Koreh. Although definitely having one person reading the whole Parsha is more dignified then splitting it between a few ba'alei Kri'oh, it is hard to say that this is a fixed Minhag Ashkenaz, and there are many Kehillos that it is split.

Michael FRBSH