250 years on from Speed's Map, this beautiful chromolithographic print (highly detailed in the original) by John McGahey shows Chester still largely contained within the ancient girdle of its city walls, and the town is still surrounded by fields.

This astonishing work was produced from a balloon tethered above the eastern suburbs of the city, probably near the junction of Hoole Lane (close to where these words are being written) and Boughton. How long it took to complete is anyone's guess.

You can follow the course of the River Dee as it curves round the Roodee to the busy Port of Chester. It then executes a sharp bend: this is the place where the old, silted up, course of the river was altered to form the New Cut in 1740.

Four bridges cross the Dee; in the foreground is the Queen's Park Suspension Bridge, built in 1852 to join the city to the affluent suburb of Queen's Park, then being created across the river. The bridge was rebuilt in 1923, and is with us still- indeed, it underwent a thorough restoration only last year.

Next is the medieval Old Dee Bridge- built, in its present form, around 1387, but standing on the site of numerous earlier wooden bridges and a Roman (and earlier?) fording place. For centuries, this was the sole crossing from Chester into Wales.

Beyond that is Thomas Harrison's magnificent Grosvenor Bridge of 1833, then the widest single arch anywhere in the world. You can clearly see how the new road to the bridge, Grosvenor Street, was driven diagonally across the ancient street layout- the first change to Chester's major roads in centuries.

Finally, at the top of the picture, the bridge carrying the railway into North Wales, which opened in 1846, can be seen.

On the right, the Shropshire Union Canal runs, as today, beneath the Roman North Wall and Phoenix Tower, and there appear to be cows grazing on the Deanery Field. Above that, another large area of open land with the walls, where the Infirmary now stands, was anciently known as Lady Barrow's Hey- 'hey' being a Saxon name for a field enclosed with hedges. Earlier still, the land was used by the Romans as a cemetery and many graves were uncovered when the hospital was being built and enlarged.

Dominating the foreground is the great medieval tower of St. John's Church, which was to collapse just 25 years after the drawing was made. Next to it, the road entering the walls passes around the site of the largest Roman amphitheatre in Britain- still at this time lying forgotten beneath the ground, but its circular shape is nontheless clearly visible from the air. It was not 'officially' discovered until 1929.

John McGahey was born in 1817. By 1844, he was listed in a trade directory as a "lithographic artist and printer" at 15 Lord Street, Liverpool. He came to Chester around 1853 and was soon listed as trading as "John McGahey and Son" at Bold Place, Chester. He produced his 'view from a balloon' during this period.

Incidentally, the earliest manned balloon flights over Chester had taken place as much as eighty years earlier, in 1786, by one Thomas Baldwin, who recorded and illustrated his experiences in his book Airopaidia.

Now go on to view a series of enlarged sections from McGahey's wonderful illustration: