The representation of towns in parliament was founded upon two principles--of consent to public burthens, and of advice in public measures, especially such as related to trade and shipping. Upon both these accounts it was natural for the kings who first summoned them to parliament, little foreseeing that such half-emancipated burghers would ever clip the loftiest plumes of their prerogative, to make these assemblies numerous, and summon members from every town of consideration in the kingdom. Thus the writ of 23 E. I. directs the sheriffs to cause deputies to be elected to a general council from every city, borough, and trading town. And although the last words are omitted in subsequent writs, yet their spirit was preserved; many towns having constantly returned members to parliament by regular summonses, from the sheriffs, which were no chartered boroughs, nor had apparently any other claim than their populousness or commerce. These are now called boroughs by prescription.[258] Besides these respectable towns, there were some of a less eminent figure which had writs directed to them as ancient demesnes of the crown. During times of arbitrary taxation the crown had set tallages alike upon its chartered boroughs and upon its tenants in demesne. When parliamentary consent became indispensable, the free tenants in ancient demesne, or rather such of them as inhabited some particular vills, were called to parliament among the other representatives of the commons. They are usually specified distinctly from the other classes of representatives in grants of subsidies throughout the parliaments of the first and second Edwards, till, about the beginning of the third's reign, they were confounded with ordinary burgesses.[259] This is the foundation of that particular species of elective franchise incident to what we denominate burgage tenure; which, however, is not confined to the ancient demesne of the crown.[260] [Sidenote: Power of the sheriff to omit boroughs.]