Artaxerxes had three sons by Statira--Darius, Ariaspes, and Ochus.

Of these Darius, as the eldest, was formally declared the heir.

But Ochus, ambitious of reigning, intrigued with Atossa, and sought to obtain the succession by her aid.

So good seemed to Darius the chances of his brother's success that he took the rash step of conspiring against the life of his father, as the only way of securing the throne.

His conspiracy was detected, and he was seized and executed, Ariaspes thereby becoming the eldest son, and so the natural heir.