Pit alignments are a little-known type of prehistoric monument found throughout the British Isles, the function of which is at present poorly understood. They consist of a series of evenly spaced and often relatively shallow pits arranged in lines. These monuments are most frequently discovered through aerial photography, being morphologically well suited to identification by this method. Some alignments run for large distances, in straight or curving lines, and clearly represent massive undertakings by large numbers of people or by smaller numbers over long periods of time."

Source : Wikipedia

Their original purpose is unknown - theories include uses as agricultural boundaries, or for some kind of ritual use.

Example research publication : Prehistoric multiple linear ditches and pit alignments on the route of the Oakham bypass, Rutland Transactions - Leicestershire Archaeological and Historical Society 81 (2007): 1.