Kind of but not entirely true - I will defer to real historians but roughly it breaks down like this 100 - 180 AD : golden age of emperors, what we think of when we think Rome

200-350 : serious decline and infighting, split into four regions, during this period attempts to enforce price controls to stem inflation. Rome itself stopped being political centre

350-400 Constantine recovery (unites to one region again - one empire of three parts, one god of three parts, one emperor - gettit?)

400 + : total collapse of western empire - communications fail, smaller regions contest with each other, and inflation wrecks the value of economies as trade collapses. Eastern empire carries on with vastly reduced army and trade links to Persia.

This really was a dark ages - impoverished, illiterate, backwards looking and lacking trade with most of the world. There was no single definition of dark AGRs - mostly because there are few ways to be right and many ways to be wrong In short, the glory of empire did not last as long as everyone thinks - mostly Rome was a trade agreement that everyone else was keeping up in lieu of anything better.