Among all 17 railway stations in Nanjing, passenger rail service is mainly provided by Nanjing Railway Station and Nanjing South Railway Station, while other stations like Nanjing West Railway Station, Zhonghuamen Railway Station and Xianlin Railway Station serve minor roles. Nanjing Railway Station was first built in 1968. In 1999, On November 12, 1999, the station was burnt in a serious fire. Reconstruction of the station was finished on September 1, 2005. Nanjing South Railway Station, which is one of the 5 hub stations on BeijingShanghai High-Speed Railway, has officially been claimed as the largest railway station in Asia and the second largest in the world in terms of GFA (Gross Floor Area). Construction of Nanjing South Station began on 10 January 2008. The station was opened for public service in 2011.

Answer this question, if possible (if impossible, reply "unanswerable"): When was the Nanjing Railway Station originally constructed?
1968