earthworks made up of banks and ditches, called ya in the Edo language in the area around present-day Benin City, the capital of present-day Edo, Nigeria. They consist of of city iya and an estimated in the rural area around Benin. Some estimates suggest that the walls of Benin may have been constructed between the thirteenth and mid-fifteenth century CE and others suggest that the walls of Benin (in the Esan region) may have been constructed during the first millennium AD. History First encounters and records The Benin City walls have been known to Westerners since around 1500. Around 1500, the Portuguese explorer Duarte Pacheco Pereira, briefly described the walls during his travels. In Pereira's Esmeraldo de Situ Orbis, 1505, we read: Another description given around 1600, one hundred years after Pereira's description, is by the Dutch explorer Dierick Ruiters. Pereira's account of the walls is as follows: The archaeologist Graham Connah suggests that Pereira was mistaken with his description by saying that there was no wall. Connah says, "[Pereira] considered that a bank of earth was not a wall in the sense of the Europe of his day." Ruiters' account of the walls is as follows: Construction Estimates for the initial construction of the walls range from the first millennium to the mid-fifteenth century. According to Connah, oral tradition and travelers' accounts suggest a construction date of 1450–1500. It has been estimated that, assuming a ten-hour work day, a labour force of 5,000 men could have completed the walls within 97 days, or by 2,421 men in 200 days. However, these estimates have been criticized for not taking into account the time it would have taken to extract earth from an ever deepening hole and the time it would have taken to heap the earth into a high bank. It is unknown whether slavery or some other type of labour was used in the construction of the walls. Description The walls were built of a ditch and dike structure; the ditch dug to form an inner moat with the excavated earth used to form the exterior rampart. The Benin Walls were partially demolished by the British in 1897 during their 1897 punitive expedition. Scattered pieces of the structure remain in Edo, with the vast majority of them being used by the locals for building purposes. What remains of the wall itself continues to be torn down for real estate