Keywords: CS: Epocha, DA: Æra, DE: Epoche, ES: Época, FI: Kausi, NL: Tijdperk, NO: Periode, PL: Era, PT: Era, SV: Era
Quoting the in-game text: "Rail Nation consists of six eras, each of them lasting fourteen days. After that, the endgame battle between the ten most developed cities will begin."
Each era has its own set of goods and engines. In general the engines from that era can only haul goods from this and previous eras. However with a researched coupling then the next era goods can also be hauled.