From all payment of the dues or fines exacted by the king as the original lord of the soil on which they had in most cases grown up the towns had long since freed themselves by what was called the purchase of the "farm of the borough"; in other words, by the commutation of these uncertain dues for a fixed sum paid annually to the Crown and apportioned by their own magistrates among the general body of the burghers.

All that the king legally retained was the right enjoyed by every great proprietor of levying a corresponding taxation on his tenants in demesne under the name of "a free aid" whenever a grant was made for the national necessities by the barons of the Great Council.

But the temptation of appropriating the growing wealth of the mercantile class proved stronger than legal restrictions, and we find both Henry the Third and his son assuming a right of imposing taxes at pleasure and without any authority from the Council even over London itself.

The burgesses could refuse indeed the invitation to contribute to the "free aids" demanded by the royal officers, but the suspension of their markets or trading privileges brought them in the end to submission.

Each of these "free aids" however had to be extorted after a long wrangle between the borough and the officers of the Exchequer; and if the towns were driven to comply with what they considered an extortion they could generally force the Crown by evasions and delays to a compromise and abatement of its original demands.
[Sidenote: Burgesses in Parliament] The same financial reasons therefore existed for desiring the presence of borough representatives in the Great Council as existed in the case of the shires; but it was the genius of Earl Simon which first broke through the older constitutional tradition and summoned two burgesses from each town to the Parliament of 1265.