In 1794 a canal was opened between Cardiff and Merthyr Tydfil over the mountains of South Wales. This was considered one of the Seven Wonders of the World at the time. Within 24.5 miles, it rose to a height of 300 metres, requiring 49 locks. When the canal was opened in 1794, Cardiff had a population of just 4000. In 1798 the canal was extended one mile seawards and included a sea lock. The total cost to build the canal was £103,600.