By the time work started in Gravesend, the estimate of costs had already risen to more than £57,000. Dodd hoped to defray at least some of this amount by selling the chalk recovered during the excavation.
By 1801, the canal had reached Higham, four miles away. It was over 40 feet wide and seven feet deep. Work halted and at this point, Dodd seems to have left the project. A new engineer, Ralph Walker, proposed a tunnel to take the canal through to Strood. Further Acts of Parliament were required to approve the scheme and enable fundraising. Work finally restarted in 1819.
By this time, the lock at Gravesend on the Thames had been completed to admit large vessels into the basin. Tunnel construction continued with the hand tools common at the time and with some additional use of gunpowder. It was a hazardous business and several workmen were killed. By the time it was complete it had become the largest, and the second longest, canal tunnel in the UK. A large basin was dug at what is today Higham Station, to allow barge owners to wait and lower masts before their vessels were towed through the tunnel by horses.
The canal itself finally opened on 14 October 1824. In the end it cost nearly £300,000.
The stone obelisk on Canal Road was erected in 1829 to mark the half-way point on the canal and the boundary of jurisdiction between the cities of London and Rochester, after Rochester laid claim to half the water in the canal.
This obelisk was one of the largest boundary markers in the country and is made from solid granite. It stands 15 feet high.
The cities’ coats of arms are still just visible at the top of the obelisk. The inscription beneath states that the monument was erected by the ‘Right Hon. Bill Thompson, Lord Mayor of London and the Worshipful John Gibbs, Mayor of Rochester’.