It's easier to understand Lateralus before explaining Mer De Noms, so this is out of order but Mer De Noms will be next.
Lateralus covers the period roughly between 1000B.C. to 300B.C.
In this period humans were creating more advanced math, geometry, tracking planets, creating religions based on astrology, societies growing into kingdoms, and experimenting with medicines. They also began melting metal and crafting swords, shields and coins.
All the previous albums described time periods that were millenniums apart, but Lateralus, Mer De Noms, 13th Step and eMotive all happen in the same time period. Mer De Noms takes place roughly from 1500 B.C. to 500 B.C.