Roman dictators during The Republic voluntarily relinquished power and resigned from a post with absolute power after the threat had passed. Notable exception being Caesar (the end of The Republic).
Rome had a somewhat Democratic system (put aside slaves and all). They strongly believed in democratic principles against dictators, tyrants, authoritarians.
Their troops marched under the banner "SPQR", 'the Senate and People of Rome', to represent those values.
But they had aristocrats, and they weren't always exactly generous with the troops, and leaders of those troops could build loyalty with them against authority.
Julius Caser's uncle had started this, when aristocrats had grabbed a lot of land for their vacation homes and left the troops with little.
Caesar built his loyalty with the people up, and eventually was in a position to march his forces 'across the Rubicon' - a traditional barrier from the troops to prevent the military from overtaking the government in Rome, which is just what happened, as Caesar defeated all his enemies up to Pompey.
They were already starting to ignore democratic rules, like an office requiring 10 years between holding it for a one-year term being ignored, held years in a row.
The leaders, the Caesars, moved to preserve the facade of Democracy - the Senate - but changed the rules to everything done they could veto, most of the Senate was appointed by them and just became a place for social prestige to be nominated. The military still had SPQR banners, but it was a lie.
At first, it wasn't all bad, as the dictatorship of the first Augustus Caesar did some good - but quickly, there was Claudius, there was Nero et al.
It was a period called 'Pax Romana' - supposedly peaceful - but was decline and tyranny.
Human history is filled with this structure of Oligarchy, a few who benefit greatly from the rest serving them.
One of the few stronger exceptions is the American middle class's growth from FDR through about LBJ or Carter - which has largely been reversed now.
When you include debt, all the postwar gains after WWII of the middle class in the 40's, 50's, and 60's are gone.
Today, powers like the finance industry make symbolic much of our democracy, when the only people who seem able to win high office are ones loyal to the right interests.
We preserve our 'civilian authority over the military' - even when a President as prestigious as the former Allied Commander of WWII, Eisenhower, is powerless to do more to stop the military-industrial-congressional complex than to announce it to the public, when presidents seem to have to ask more than tell the military their policies at times, from Clinton blocked on allowing gays by Colin Powell to Obama's goal to end discrimination met by polling the military's opinion, votes based on the military agreeing. When the culture where FDR wanted the Pentagon to be a temporary building because a concentration of military power that close in the capitol could begin to dominate much of the civilian government is a long forgotten quaint bit of history.