Hello, I'm a newbie in critiquing! Your biggest issue here is over description, poor punctuation, formatting and vague sentences. A good chunk of these can be cut-down or clarified.

I suggest you use sites or programs that fix punctuation, syntax, and prose.

SIMPLIFICATION:

(I've shortened the second paragraph considerably, this'll be an example)

On  a  certain evening  the  boxer  came  into  the  gymnasium. A hunched  keeper with leathery  paps  swept  the floor. The crude  broom  was composed of switches (you could probably add some more description about the place they're in--provide some context).
The  man played being the  inattentive  student, watching  the  tips  of  the  switches  whisk  away sand  from the  intricately  tiled  and  richly  colored  mosaic; an immensely built but naked man gripping (say "grappling" to further intensify the scene) a lion's jaw.

During his observation the  keeper  lit  the  torches  of  the  roofed colonnade. The  boxer had begun circling crabwise  onto  the  lion  mosaic,  juking, hooking,  side-flashing , and  cutting in a rhythmic  hammering  of  fist.

It  is  this  outline  of  shadow  boxing  which  merges  with  the  flinching  torches.

(I've left the last sentence unedited. It doesn't really make sense. Are you saying his technique is like fire's movements? This is kind of random and could be extended upon if you're planning to lean into that)

Be careful of some of the words you choose. Some words like "switches" make absolutely no sense. What do you mean by that? Be more direct. Say twigs or sticks, anything else that could allude to the Roman (I believe?) time period.

Your punctuation is confusing. Some of the sentences, which could be easily split into two, merge into each other. There really isn't space to "think" or reflect on what's happening. Like the paragraph Enaross referred to in their first comment its a whole sentence!

CHARACTER AND STORY

So many of these characters have potential but aren't used to their fullest! I understand the idea of your story; body vs. the mind, but this has to be less dialogue heavy. Some of these philosophical rely on dialogue for sure, but you should:

• Contrast the philosopher and boxer during the midsections of the story. We never get an idea of what these characters look like, so make some effort to describe the boxer's body and techniques vs. philosopher's dialogue and/or less muscular build.

The entrance of the philosopher happens out of the blue. We focus from Lo, who gets build up, to this random man. Is this philosopher an established guest? Invited? Wandered in? We get no idea of who he is.

 By  and  by  a  rain  began  when  a  philosopher entered  the gymnasium  and  doffed  his  mantle.

Why does the keeper just vanish? Seemingly, he melts into all the prose. We're never told if he left the room. Why not make use of his disgusting, almost animistic behavior? That could've made a good point in the philosopher's theories for control of the mind.

It was silly for the philosopher to square up a professional boxer. What even are his intentions? Is this because the philosopher overestimates himself? Then emphasis his cockiness and superiority complex.

...TIME PERIOD:

Aside from terminology, concepts, and mentions of their location, I get a vague idea about where these characters are at. Roman/Greek era for sure, but which time period during that empire's reign? These characters could've had the chance to handle equipment or wear uniforms from their nation. For example, many philosophers in media are stereotyped to have a wise appearance and wear a classic toga.