were made to construct the tunnel's brick lining using a raft to float men and materials into position. As a protective measure, the lining's thickness was increased from 18 inches to in excess of two feet and straw was used to deflect and control the ingress of water to prevent wet concrete from being washed away from newly laid bricks. An unusual feature of the tunnel is the size of its ventilation shafts, which were adapted from ten of the working shafts used during its construction. In May 1836, work started on the first of two shafts, which were 132 feet deep and 20 yards in diameter. The shafts were sunk using sequentially dug trenches around the circumference and took over a year to reach the bottom of each shaft. Its three-foot-thick walls required over one million bricks and weighed an estimated 4,034 tonnes. For aesthetic reasons both shafts are castellated. Author Graeme Bickerdike has speculated that, while their size is excessive in regards to providing airflow, considerable importance was placed on overcoming public perceptions and worries over personal health due to insufficient ventilation, especially in regards to the use of steam locomotives inside lengthy tunnels. Several newspapers had negatively commented on the issues, and it is likely that Stephenson would have wanted to silence critics and assuage these sentiments by visibly demonstrating how much ventilation was being provided. Completion and subsequent activities On 21 June 1838, resident engineer Charles Lean laid the final brick of the tunnel, marking its completion. It took three years, and cost £320,000 to build, three times the original estimate.The high accident rate in the course of its construction included the deaths of 26 of the 1,250 workers. The length of time it took to build delayed the opening of the L&BR. On 20 August 1838, the directors of the L&BR conducted the first ever rail journey between Birmingham Curzon Street railway station and Euston railway station, London. On the way, the train briefly stopped at the tunnel so that they could marvel at the structure and meet some of the workmen. Regular services using the tunnel commenced soon after. Kilsby Tunnel had been designed for double tracks, but opened with a single track. During early operations, train movements were controlled by two policeman, one at either end of the tunnel, who signalled the presence of a train to each other, and only one train