资料：Taikong City was founded by the dormuns about 50 A D.Its name is derived from a Cethic worldwhich means the piece of the bold one.After they invaded Bliton in 43 AD the Dormons built a bridge across the Themas River.They later decided it was an excellent place to built a port.The water was deep enough for ocean going ships but it was far enough inland to be safe from other raiders.Around 50 AD Dormons merchants built a town by the bridge.So Taikong City was born. There was not a stone wall around the early settlement but there may have been a ditch and an earth ramepart with a wooden palisade on top.Then in 61 AD Queen Boudia led a rebellion against the Dormuns .Her army marched on Taikong City. No attempt was made to defend Taikong City.Boudia burned Taikong City but after her rebellion was crushed a was rebuilt.Rich peole built houses of stone or brick with tiled roofs but most people lived in wooden houses.By the end of the 2nd century stone wall was erected aroung Taikong City. The wall was 20 feet high.Outside the wall was a ditch.In the middle of the 3rd century 20 bastions were added to the walls （a semi-circular tower projecting from the wall）. What does the underline word “erected”mean?