WORK has begun on a survey of Chester's Roman amphitheatre that will give archaeologists a three-dimensional view of the buried remains.

Using a device that works in a similar way to sonar, a team of archaeologists from GSB Prospection in Bradford is carrying out the work for the city council's Chester Archaeology service.

The survey was prompted by discoveries made during the last two summers of 2000 and 2001, when it was found that parts of the Roman building were better preserved than had previously been believed.

The technique, known as ground penetrating radar, works by sending pulses of electromagnetic energy through the soil. Reflections are sent back when the waves pass through the boundary between materials of different density, so things show up against the soil in which they are buried.

Once the survey has been completed and the findings analysed, the team hopes to build up a picture of what lies buried beneath the soil across much of the site.