But, unhappily, neither was the tribute the sole tax which the crown exacted from its subjects, nor had the crown the sole right of exacting taxation.

Persian subjects in many parts of the Empire paid, besides their tribute, a water-rate, which is expressly said to have been very productive.

The rivers of the Empire were the king's; and when water was required for irrigation, a state officer superintended the opening of the sluices, and regulated the amount of the precious fluid which might be drawn off by each tribe or township.

For the opening of the sluices a large sum was paid to the officer, which found its way into the coffers of the state.

Further, it appears that such things as fisheries--and if so, probably salt-works, mines, quarries, and forests--were regarded as crown property, and yielded large sums to the revenue.