But the precautions taken against revolt did not end here. Once a year, according to Xenophon, or more probably at irregular intervals, an officer came suddenly down from the Court with a commission to inspect a province. Such persons were frequently of royal rank, brothers or sons of the king. They were accompanied by an armed force, and were empowered to correct whatever was amiss in the province, and in case of necessity to report to the crown the insubordination or incompetency of its officers. If this system had been properly maintained, it is evident that it would have acted as a most powerful check upon misgovernment, and would have rendered revolt almost impossible. Another mode by which it was sought to secure the fidelity of the satraps and commandants was by choosing them from among the king’s blood relations, or else attaching them to the crown by marriage with one of the princesses. It was thought that the affection of sons and brothers would be a restraint upon their ambition, and that even connections by marriage would feel that they had an interest in upholding the power and dignity of the great house with which they had been thought worthy of alliance. This system, which was entensively followed by Darius, had on the whole good results, and was at any rate preferable to that barbarous policy of prudential fratricide which has prevailed widely in Oriental governments. The system of checks, while it was effectual for the object at which it specially aimed, had one great disadvantage. It weakened the hands of authority in times of difficulty. When danger, internal or external, threatened, it was an evil that the powers of government should be divided, and the civil authority lodged in the hands of one officer, the military in those of another. Concentration of power is needed for rapid and decisive action, for unity of purpose, and secrecy both of plan and of execution. These considerations led to a modification of the original idea of satrapial government, which was adopted partially at first--in provinces especially exposed to danger, internal or external--but which ultimately became almost universal. The offices of satrap, or civil administrator, and commandant, or commander of the troops, were vested in the same person, who came in this way to have that full and complete authority which is possessed by Turkish pashas and modern Persian khans or beys--an authority practically uncontrolled. This system was advantageous for the defence of a province against foes; but it was dangerous to the stability of the Empire, since it led naturally to the occurrence of formidable rebellions. Two minor points in the scheme of Darius remain to be noticed, before this account of his governmental system can be regarded as complete. These are his institution of posts, and his coinage of money.