To the south of Monks Mound is the Grand Plaza, a large area that covered roughly and measured over in length by over in width. Researchers originally thought the flat, open terrain in this area reflected Cahokia's location on the Mississippi's alluvial flood plain, but instead soil studies have shown that the landscape was originally undulating ridge and swale topography. In one of the earliest large-scale construction projects, the site had been expertly and deliberately leveled and filled by the city's inhabitants. It is part of the sophisticated engineering displayed throughout the site. It was used for large ceremonies and gatherings, as well as for ritual games, such as chunkey. The game was played by rolling a disc-shaped chunky stone across the field. The men would throw spears where they thought the chunky stone would land. The game required a great deal of judgment and aim.