ROME (Reuters) -Workers broke through a final, thin veil of rock on Thursday, opening an underground tunnel between Austria and Italy that will eventually become a high-speed rail line linking the north and south of Europe. The Brenner Base Tunnel, which is being billed as the world's longest underground rail connection, is a centrepiece of a European Union drive to shift freight off the roads and onto rail, to cut pollution and boost cross-border trade. "Today we are taking together a decisive step for the construction of one of the largest infrastructure works in the entire continent," Italian Prime Minister Giorgia Meloni said at the rock breaking ceremony.