Robert Vazie was a mining engineer who had tried to cut a tunnel below the Thames at Rotherhithe, nearly forty years before Brunel achieved this task. In 1808, believing the soil in the area to be even and solid in formation, he proposed to build a tunnel through the hill. From Shepherd's Hill one would have seen the same fields as before, with Archway Road sloping down between the fields to a tunnel mouth, with an unchanged Hornsey Lane running high above. A Turnpike Trust resolved to follow Vazie's advice and by-pass Highgate Hill by building a tunnel through the escarpment, below Hornsey Lane. After a long, steady climb the road would skirt Highgate Hill along the dip at Shepherd's Hill as it does today, and then it would go on to meet the old North Road at the Wellington.
An Act of Parliament was passed, allowing work to be started but by 1811 Rennie, as consultant, was expressing doubt about the quality of the brickwork. On 13 April 1812 disaster happened. The tunnel fell in below Hornsey Lane with a crash like thunder and the road became impassable. Underground water and the unstable joint between the clay and the loam lying above it, probably caused the collapse. It is said that the workmen had been predicting trouble for a fortnight, but fortunately nobody was hurt in the collapse. A crowd of 800 people came on Sunday to view the ruin.
Within three days the Directors of the Highgate Archway Company had resolved to build the road as an open cutting, with a stone arch to support Hornsey Lane. The architect for the bridge was John Nash, who may also have buttressed the flanking walls. The structure consists of a series of race-track arches supporting the central arch on either side. Thus the round road twuiel was only one of a number of very similar arches and Hornsey Lane was supported like a canal viaduct spanning a valley, except that only the central arch was open and all the rest were buried in the surrounding earth. The structure could equally well have suited a viaduct carrying a canal, a railway, or a road across a valley.
The foundations of the bridge were completed by November 1812 and Hornsey Lane was re-opened to traffic in August 1813. Archway Road had a gradient of 1-23 to 133, much easier than Highgate Hill, but the road surface was so bad for a time that some hauliers changed back to the Highgate Hill route. It was only when Telford dug out the old road surface and laid new drains and a concrete foundation, that the road became really popular. Archway Road made history by being the first road with the thick concrete foundations, consisting of gravel and Roman cement, which we take for granted today. Before this roads had been made of crushed stone and had none of the firmness which is given by concrete.