The metro network of Portugal's second largest city, whose Alfama UNESCO has declared to be a World Cultural Heritage, is 70 kilometers long. The alignment of new sections of the Lines C and S were planned to cross under the historic city. In 2000, two Earth Pressure Balance Shields set to work for this job. Tunnel construction under the streets of Porto proved to be a really tricky operation. The EPB Shield S-203 completed the Line-C-Tunnel without any major interruptions in October 2002. Excellent advance rates of 18.2 meters per day were recorded. Line C was officially put into operation in January 2003. In Autumn 2003 EPB Shield S-160 completed the second tunnel.