In 1101 Henry I granted royal fees to the town, meaning they collected the royal fees [dues, taxes] instead of the sheriff and there was a similar grant by Henry II in 1185. In 1201 (8th January) King John granted a charter authorising a Guild of Merchants and various other privileges, including an annual fair in Rogation Week at the port of Reach, still opened by the Mayor of Cambridge. This charter cost them 250 marks, a very large sum. It still didn't exclude the sheriff but a second charter in 1207 (for another 250 marks) provided for the election of a reeve (which evolved into mayor by 1231) as an independent town, in charge of its commerce, and granted the royal fees in perpetuity.
The sheriff and county justices of the peace still had responsibility for law and order. There were four town bailiffs, one for each Ward (Bridge, Market, High and Mill), elected annually. The town contained about 500 buildings and there were no public buildings (other than churches). The frequent river floods swamped most of the town, only the "hills" (Market Hill, Peas Hill etc.) staying dry.
The town burgesses, mostly farmers with some traders and artisans, finally got the concession from King Henry I that the borough of Cantebruge should have a monopoly of loading and unloading boats in the county and a similar monopoly on carts and that tolls should be taken nowhere else. [The county was just a roughly oval-shaped area centered on Cambridge at this time - the Isle of Ely, including Wisbech, was separate.]
There were confirmatory charters in 1227 and in 1256 the town was freed from the administrative control of the sheriff. Curiously the mayor was granted a seal but the town didn't receive one - a common seal - till 1423.
Towards the end of the thirteenth century and throughout the fourteenth the poor administration of the town led to the Chancellor receiving more and more power and the town becoming subordinate.
Queen Elizabeth issued a charter for Sturbridge Fair in 1589, granting the town the profits and booths. This ended a long period of rental from the Crown. It also contained regulations for the layout of the various sections of the fair, which are reflected in the modern street names in the area such as Mercer's Row.
The town paid yet again (£90) for a new charter for the Borough of Cambridge in 1605 but it still had the crucial clause saying that nothing in the charter shall infringe the privileges, liberties and profits of the University.
In 1610 and again in 1616 the town petitioned for city status but was refused as they tried to infringe the University's privileges in their proposed charters. They finally got it in 1951.