NEWPORT is criss-crossed by bridges and tunnels - the demolishing and re-building of some is causing great disruption now. Martin Wade tells the story of these often overlooked, vital artieries which keep Newport moving.

A clutch of crossings in the heart of Newport tell a story of how engineering miracles were made in the teeth of adversity, with great skill and with great risk to life and yet are scarcely thought of now.

They all help traffic flow and cross great barriers. One carries trains across the Usk, one traffic over the railway and one allows trains to thunder beneath Stow Hill.

Any review of crossings in this part of the world must mention one name – Isambard Kingdom Brunel.

When he came to survey Newport in the late 1840s, the great engineer who built the line from London across South Wales to Swansea, had to devise a way to cross the Usk.

He designed a 1,200 ft-long timber viaduct with eleven spans. Vast amounts of wood with each timber immersed under pressure in creosote to proof them against the elements.

When the bridge was on the verge of completion on May 31 1848, disaster struck. It may have taken two years to build, but in six minutes, the whole, fantastic structure was engulfed in flame after a red-hot iron used to rivet the timbers together had ignited one of the beams which were soaked in flammable creosote.

Brunel then had to work fast. If he started to build a new bridge from scratch, the opening of the line would be delayed. He sketched out a design using girders and wrought-iron plates. Timber was used again, but this time, he had the wood fire-proofed using a process called chyanizing.

The bridge was ready by 1850 and the line was driven on. It lasted until 1925, having given seventy years of service and was replaced by a four-track crossing which still stands today.

But the Usk was not the only obstacle to Brunel's plans. As the line was drawn on the map, snaking through Somerton, over the Usk, over the canal where Heidenheim Drive is today, it would come to another immovable obstacle on leaving the station. Stow Hill overlooked the town with the then St Woolos church atop. It had to be got around or avoided.

Originally called the Hillfield railway tunnel and at 770 yards it is a mere tiddler compared to Gwent's other great Brunel tunnel – that running beneath the Severn, which stretches for 7,668 yards. But each of those 770 yards exacted a heavy price in sweat and toil.

Hundreds worked to dig the tunnel under Stow Hill. By 1850 across the UK, more people than served in the Royal Navy and the Army - a quarter of a million, worked digging tunnels, cuttings and laying 3,000 miles of railway line across the country.

Engineers may have designed the railways, but it was left to these vast gangs of navvies to build them. The word ‘navvy’ came from the ‘navigators’ who built the first ‘navigation canals’ in the eighteenth century.

Itinerant workers who tramped from job to job, they lived and worked in appalling conditions in makeshift shelters alongside the bridges and tunnels they worked on. The site of what would have been their home in Newport was marked until recently by the name of the pub which overlooked the tunnels, called ‘The Engineers Arms’. In the 1840s there was no compensation for death or injury and engineers like Brunel refused to give them adequate housing and sanitation, or safer working conditions.

It took the building of the Woodhead Tunnel through the Pennines, which saw many tunnelers killed between 1839 and 1852, before a Parliamentary enquiry found that conditions must be made safer.

However, Brunel pioneered an efficient way of tunneling while protecting those doing the digging.

Brunel's tunneling shield was a scaffold with a space for diggers to hack away at the face of the tunnel while being protected from falling soil and rock. The temporary frame would be at the head of the tunneling drive, giving temporary support before the sides could be secured by lining with brick or iron.

Brunel is said to have been inspired in his design by a mollusc, called the 'shipworm' or Teredo navalis. The creature is protected by its shell as it gnaws its way through boat timber or wooden piers.

The tunnel was completed in 1848 although the track wasn't laid straight away. Many would walk through the tunnel and marvel at the work the navvies had done ploughing this passage deep beneath Windsor Terrace, Clyffard Crescent and Stow Park Avenue before emerging, blinking into the sunlight near Llandaff Street just off Cardiff Road.

The tunnel was finished with a round-headed arch on both ends faced with rock in style influenced by 16th Century Italian architecture. The first scheduled trains rain through the tunnel in June 1850, with excursions running to London to see the Great Exhibition. An unremarkable journey made several times a day today would have then presented an array of engineering miracles. The journey to the capital would have been as fantastic as a tour around the Great Exhibition – the showcase of British industrial and scientific might.

A second tunnel was added in 1912.

By the time the current bridge over the railway was laid in Bridge Street in 1911, conditions for workers had improved enormously.

Steam power, although available before, now had become cheap enough to replace the shovel and brawn for many jobs. Just as the Severn Tunnel dwarfed that under Stow Hill, so the challenge to build the Bridge Street crossing must have looked a small one.

While the Usk bridge at 1,200 feet needed all Brunel’s expertise, this bridge was a simpler affair. The lattice, or criss-crossing design helps prevent the bridge girders from bending. This simple and functional design has done its job and kept traffic flowing over the railway for 105 years.

Although many will give them a second thought, these great structures, which we use everyday and help keep our city moving, serve to remind us of the great skill, hard work and sacrifice to create them.