In recent years, China has been partnering with African countries on the construction of ports, bridges and other infrastructure projects. In fact, the foundation of friendly ties between African states and China can be traced back to a major infrastructure project that was built nearly 50 years ago. Yang Chengxi reports from Tanzania's port city of Dar es Salaam, where the Tanzania-Zambia rail line can be found. He will ride on a train that's barely changed for half a century to try to understand why it was built against all odds and to witness the impact it's still having to this day.