A cricket field is a roughly elliptical field of flat grass, ranging in size from about 90 to 150 metres (100-160 yards) across, bounded by an obvious fence or other marker. There is no fixed size or shape for the field, although large deviations from a low-eccentricity ellipse are discouraged. In the centre of the field, and usually aligned along the long axis of the ellipse, is the pitch, a carefully prepared rectangle of closely mown and rolled grass over hard packed earth. It is marked with white lines, called creases.