Their tactics maybe inspired by ancient military tactics but their they certainly aren't organized at all like Roman legions, nor do they operate like them. The organizational structure matters quite a bit since that's what made legions special in the first place.

South Korean riot police use modern crowd suppression methods that are meant to halt and contain large groups of people, and at best only resemble Roman tactics.

And they get a LOT of practice. South Korean opposition groups, activists, and labor unions are very prone to large, militant demonstrations and often organize with the intent to riot.

Also, it's important to remember 2 major things.

One, there are specific military units that are often called up to supplement standing police riot forces. Generally when things get out of hand, it's the actions of these military units that are usually made of young, inexperienced men as opposed to the professional riot police. But no doubt, they are trained and organized.

Two, military service is mandatory for South Korean males. And many of them end up serving in these riot police supplement units. They are there because they have to be and while their numbers are important to containing otherwise escalating and overwhelming situations, their use is questionable when not properly managed and supported by core police units with experience in handling large crowds.

South Korea itself has a very long history of very militant activism, which culminated in the riots directly prior to the 1988 Seoul Olympics, which won modern South Korea it's current democratic process, halting the decades of successive dictatorships. This is also when South Korea was recognized on a global stage and was making its transition from moderately wealthy developing country in the region to one of the most prosperous countries in the entire world.

In many ways, the 1988 Seoul Olympics were a major turning point for South Korea.

Anyways, the modern iteration of South Korean riot police is very restrained compared to what it was like pre 1988 Seoul Olympics.

Riot police often very brutally put down protests, resulting in what many people refer to as the Gwanju Massacre in 1980, or the spectre of being whisked away in the night, imprisoned indefinitely, and being subjected to physical abuse and torture.

The police could and would conduct raids on residences, work places, and offices to arrest and detain opposition of the government, particularly those suspected of being Communist or North Korean sympathizers/agents. Very much like the Red Scare in the West, it was often a convenient excuse for dictators to label political opponents as enemies of the state, and the police were often implicit in these abuses.

Even today, opposition groups and labor unions can and are the targets of police raids for organizing illegal protests (not obtaining permission to hold a protest, particularly if they descend into riots, as they often do).

Many of what the South Korean riot police do as a matter-of-fact in their crowd suppression tactics would definitely be considered major abuses in the US and Europe, particularly if fighting breaks out.

That being said, in general, protests/riots in South Korea are generally much more organized, especially labor unions which are extremely well organized and militant. Many of the organizers of these demonstrations are veterans of decades of protests and know how to fight against the police.

Occupations of factories and businesses by strikers are very accurately called 'sieges'. Riot police and demonstrators often do fight, which is against orders and doctrine of the riot police (because it escalates the situation when they want to de-escalate it) but emotions tend to run high on both sides, particularly when the opposition is organized and can cause real casualties to security forces.

For example, in one riot in 2002, strikers advanced on riot police formations with a line of psuedo flamethrowers, albeit with very little range. Strikers then followed up with a short charge at police before breaking back off.

In general, fire is the main weapon used against security forces, along with thrown objects, since guns are incredibly hard to get a hold of.

Also, experienced rioters in South Korea are incredibly resilient to water cannons. I've seen columns of strikers stand tall against a water cannon, which is just insane.

Anyways, South Korean demonstrations and riot police/military are very interesting and very different compared to your average US demonstration because of the propensity to descend into violence very quickly, which everyone kind of accepts as a fact of life in South Korea.

If you have more questions, I'd be happy to follow up.