During 1871, construction of the Gotthard Tunnel proper commenced, it would take ten years to complete. Boring was commenced from both sides simultaneously, being reliant upon accurate surveying to keep each bore in alignment with one another. Amongst other feats, the boring process involved the first large-scale use of dynamite, a relatively recent innovation that had only been patented in 1867. Another key innovation was the use of mechanised tunneling machines, which the Swiss engineer Louis Favre, supervisor of the work as well as prime contractor, strongly advocated for despite some pressure to make greater use of manual boring. The engineering used to created the tunnel can be largely credited to Favre, although he was unable to see its completion, having suffered a fatal heart attack while inside the tunnel on 19 July 1879, barely six months before breakthrough would be achieved.