It was October 27, 1904 when the first underground line of the New York City subway opened. The construction methods at the time involved digging up the earth, digging the tunnel, building the subway and then re-covering the construction. The street would then be re-built. However, eventually boring machines began to be used to tear through hard bedrock and under the rivers. Today, the New York City subway operates 24 hours a day, 7 days a week, one of the few major city subways to so operate.