filled by a small seasonal river during the rainy season and continues to hold enough water for it to be used by archaeologists in modern times. Thirteen reservoirs have been identified at Calakmul. The combined capacity of all the reservoirs is estimated at over . This quantity of water could have supported 50,000 to 100,000 people; there is no evidence that the reservoirs were used to irrigate crops.Aguada 1 is the largest of the reservoirs and has a surface area of . Causeways Eight sacbe (causeways) have been located around Calakmul. Two of these have been mapped, three have been identified visually on the ground and three more identified with remote sensing. They have been numbered as Sacbe 1 through to Sacbe 7. The causeway network not only linked Calakmul with local satellite sites but also with more distant allies and rivals, such as the great cities of El Mirador, El Tintal and Nakbe. Those causeways that cross swampy land are elevated above the surrounding wetland and they now tend to support denser vegetation than the surrounding forest.Sacbe 1 is long and is lined and filled with stone. It is located within the mapped urban area of the site core. Sacbe 1 was first mapped in the 1930s by the Carnegie Institution of Washington.Sacbe 2 is long. It has been mapped within the urban area of the site core. Sacbe 2 is built of packed earth and was discovered during the archaeological excavation of a nearby quarry. This causeway may have been built to transport stone from the quarry in order to build Structures 1 and 3.Sacbe 3 extends northeast from the site core and is visible from the summit of Structure 1. It was first discovered in 1982.Sacbe 4 runs southeast from the site core, it is also visible from the summit of Structure 1 and was discovered in 1982.Sacbe 5 runs westwards from the main watering hole, across El Laberinto seasonal swamp and carries on for a total distance of or more towards Sasilhá.Sacbe 6 runs southwest across El Laberinto bajo and links Calakmul with El Mirador ( to the southwest) and, beyond it, El Tintal (an additional .Sacbe 7 is located south of Sacbe 6. It is at least long and runs across El Laberinto swamp.Sacbe 8 is on the west side of the swamp and does not appear to cross it to the site core. StructuresStructure