Hi Shearluck
This may look bad, really really bad, but there are really not that many things to fix and I did enjoy reading the chapter even with the few nits I picked up. So pull on your armour and take a deep breath!
I'll give you the detailed nits/suggestions and then I'll end with what I think the bigger picture issues are, and if you agree, at least you would have an idea where to start!
[delete] (add) *comments*
Silas Tyrn sat on his blood(-)red warhorse watching [as] the sun sank below the great hills to the west. The trees on either side of him [cashed](casted) eerie shadow(s) over the other men under his command.
* really good start!
Each sound sent an icy trail of *fear*through Silas.
* not sure this is exactly the right word here because if he is the hero, I don’t mind them anxious/careful, but I do mind them scared
* then I got to his age – might want to let us know first he’s young, because then readers will understand and forgive
His hands gloved in black leather and ring mail, felt frozen[, a](. A) biting chill swept through them all.
The river that lay across the fields, known as the *Val’thren*, was completely iced over.
* nice!
No [sigils](signals) or banners could be seen, just [50](fifty) men atop horses, and another [60](sixty) on foot, holding long bows made of yew. Silas sighed[; he](and) felt all the weight of his 16 years on his shoulders.
* check, there are rules when to use numbers and when to write it out, but from memory, the latter applies for numbers smaller than 100, and you need to ensure your use of numbers is consistent
Like him the men were lightly armored[,](in?) hardened leather and ring mail. Each bore a long sword, spear, and shield[,](.) (Grey and black.) [no](No) crests adorned them[, just more grey and black]. The sun finally set[, to the south], the watch fires of King Valinor’s army burned brightly[,illuminating] (to the south and illuminated) the massive wooden fortress.
It wasn’t fully manned; the King(‘)s true strength would not be here for another [6](six) hours. The rebels did not think *they* would be there for another [3](three) days.
* who are they, Silas and his men?
* overall, so far, you’re nailing putting us in the right time and place!
Silas’ elder brother *sat* in the keep waiting as wel[l](.)
* not sure sat is the right word here, see if you can’t tell us exactly what he is doing otherwise I’m going to picture him with some embroidery! 
[, his](His) elder brother was [20](twenty), muscled like a bear with a temper to match.
His name was Rhanos, first son of Lord Thanal Tyrn, who was [Second Son,](the second son) of Huron Tyrn, Warden of the South.
* consider only referencing to Huron as the Warden of the South at this point and if required, hit us for his full name when he arrives in a scene?
A bird suddenly cried out, a great caw caw caw. The men stiffened when they heard it[,](as) they knew what it meant[, the](. The) rebels would be crossing the river soon. Not long after came the sound of muffled feet[, a]. (A) great deal many muffled feet.
“The scum are nothing if prudent,” Spat Ser Rollin[, scratching](and scratched) at his great red beard.
* try avoiding –ing words where you can, but not at all cost or always
Ser Rollin was a large man of about [35; he](thirty-five and) had trained Silas ever since [he](the young boy) *I can be pedantic like this
* could hold a sword. Having him there helped ease the young Captains nerve(‘)s[,](.)
Silas smiled under his leather mask and whispered [back], “When did you learn what [Prudent](prudent) meant?”
Ser Rollin snorted, and shook his head saying no more. Silas was sure that had earned him a good thrashing next time they sparred, if either of them survived (this day?).
The pleasant feeling [Silas had] quickly rolled away[,] as three lines of infantry fully *crossed* [over] the river.
* consider marched or something like that – crossed could make some readers forget all about the ice!
* yes, I’m really finicky today! 
Most were mercenaries[,] and peasant soldiers, (or) what his father liked to call the[,] ‘meat’ of the Rebel army.
The lines marched [bellow](below) [their](who exactly because we have a lot of groups around) position[,](.)
* not sure this is really needed?
Silas was to charge the back of the enemy while his brother led a sortie from the camp[;](, and) they were to hold until the King’s army joined them.
[Suddenly there was a](A) horn blast(ed) (unexpectedly) from in the camp[ and](. Followed shortly by) a shower of arrows [fell](falling) among the unsuspecting rebels. [Silas could hear their screaming](Their screams) carried on the wind, [it sent](and send) a chill through him.
The lines of rebels let out [a] shout(s) and [began to] surge(d) forward [toward the camp].
He angled his spear lower as the trot turned to a full gallop and then a charge[, some](. Some) of the rebels began to turn [hearing](when they noticed) the sound of hooves over the sounds of fire and battle. It was too late[, the](. The) charge bit into the back of the formation and drove into it. Silas felt his spear pass through a man(‘)s back [as with was](and) wrenched loose from his hand.
* believe the technical review term for this would be “hard core”! That must hurt!!!! Make it double hard-core! 
He drew his sword, and slashed down at another man who had been knocked back by a horse. Blood coated his blade[,] and arm[,](as or while) sweat poured from his brow[, his](. His) breathing [was] ragged, [and] Silas had never felt better.
He cut the hand off a man running towards him with an axe, and reversing the blade [he] sliced [him across] his unarmored gut. Despite their superior numbers(,) faced with fire[,] and a charge of [50](fifty mounted warriors) [horse](,) the rebels broke and made for the river. Silas grabbed a great horn and blew a blast into it(.) [as](As) one his men turned and broke away from the tangle [of men at](. Their full gallop[, sending](sent) chunks of frozen turf into the air
* not sure who is galloping here, Silas’s men or the rebels?
The sudden retreat of the horses seemed to [have some] change [over] the men[, some](. Some) continued to run, but others cried out (the) names of companions[,] or simply just cried as they ran after the horsemen, mad with blood.
As the company came together(,) they slowed (their) pace, keeping just fast enough to avoid the men afoot. [Then, as] Silas and his men neared the hill[;](and) [ they] spurred their horses hard(,) leaving their pursuit to struggle on after. Silas blew his horn again[,] and a volley of arrows sprang from the trees [and landed](, landing) among the tired rebels. Silas called a halt (a little way up the hills to)[, and] re(-)organize[d] his men[, a little way up the hills,] while the archers fired again. [To his eyes Silas could see](Silas’s gaze followed?) at least 300 men running through (the) arrow fire, wait no, 298, two had just stumbled, and succumbed to wounds.
* funny as!
He called to a nearby man, Donnel [he thought].
* I don't understand, isn't Silas sure his name is Donnel?
“Yes(,) [M](m)’lord?” Donnel asked, breathing heavily, an arm hung limp at his side[,](.) Silas eyed him up and down once before saying anything[,](as) another volley [leaving](left) the trees[ and](,) striking [at] the scattered men.
“Gather up the wounded and bring them back behind the archers[, then](. Then) tell Brigon to hold as long as he can, [and then](before he and his men) scatter through the woods and pick off men [where he can](at will)[,] [be](Be) ready to ride away if it [go’s](goes) ill.”
[Silas said, the] (The) man nodded and began calling for those with wounds to ride up with him. Silas now had [40](forty) riders in good condition, and his bowmen('s quivers were still full.[ seemed to not be running low on arrows].
“Orders Lord Tyrn?” [He](he) called, holding [up] his spear in (a) salute.
Silas closed his eyes for a moment before speaking[,](.) “Once the enemy is [100](one-hundred) yards away[ spilt](, split) one [Unit](unit) [for](between) yourself and [one for] me[, ride](You and your unit go) [out and] around and come up from the rear[, funnel](. Funnel) them towards the river if you can[, be](. Be) prepared to break away and charge again, we’re light enough to pull away if need be.”
* break your sentences into shorter sentences to resemble orders being given during a battle
[Silas barked in his best commander voice, the one he had always practiced when he had been younger.]
* I don't think this is needed if you use the shorter sentences – I don't think the back info is required right now and it only serves to interrupt the flow of an otherwise tight action scene!
The decision [had been] made[,] and the troops ordered, [Father](his father) would have been proud[,](.) (Even) Ser Rollin might [have even been](be) proud, (but) it was hard to tell.
The Rebels [had] organized(repositioned) into a tight box formation, holding their shields high as they advanced. [The Rebels](Their) marched quickened as they neared the [horseman](horsemen), roaring in high voices, they sang as the(y) broke out into a run.
At [100](one-hundred) yards(,) Silas blew a blast on his horn once more(.) [and the](The) blast echoed through the trees, and the forest seemed alive with the sounds of answering calls. The [Rebels](rebels) * unless it's their name name* faltered and hesitated, fearing that they had again been [lead](led) into a trap(.)[, and great knights with their fell lances lay just in the woods]*can the rebels see them? Consider letting them rather appear in the scene than having the rebels guessing?*
They nearly fell back when Silas and his men rode past their left, hurling spears into their unprotected sides. They turned to protect themselves(,) only to be taken by another rain of black arrows (from where?). [The Rebels were in confusion,](Confused, the rebels) half broke off to fight the horsemen [and](while) the other half [split] continued along towards the hill.
Silas met the other half of his company, and immediately blew a blast on his horn to sound the charge[,](.) [from behind](Behind) him(, from)[ in] the direction of the fort, there was an answering blast.
His brother had won the other side of the fire and was on his way.
* not sure what is meant by fire in this context?
Silas spurred his horse harder, finally smashing into the line of rebels like a scythe through grass. He slashed at all sides[ and found](finding) [a] target(s)[,] (and) mowing them down with frightful ease. Suddenly there was a sharp yank and Silas was flung from his saddle. He hit the ground[,] hard(,) [and the] (his) breath [was] blown from his body.
Silas *glanced* the blow aside with his shield and [brought](drove) his blade strait into the man’s throat.
* not sure glanced is the right word here ... can't think of the right word at the moment though, sorry
[Everything seemed to move so slowly to Silas, he] (He) parried a blade aimed at his head and bashed the swordsmen’s face with his shield. A large man with an exe brought it down hard on his shield and splintered it[,](.) Silas fell back(,) roaring in pain, and [tossing](tossed) the wreckage [of his shield](or consider the wrecked pieces of his shield) to the ground.
*Suddenly* a great pain ripped through the young commander’s head and he fell to the ground[,](.)
* need another word here – I think you've used it a couple of times already
[ a](A) man [stood](halted next to him and towered)[towering] above him [holding](,) a stone masons hammer (raised above his head or in his hand).
Silas wasn’t looking at the man[; he](. He) was looking above him into the pale light of the stars.
* consider letting the reader know much earlier it's night – up to this point, the sun was shining very brightly in my mind!
* make it clear that Silas fell on the ground (fall back isn't enough)
[They shimmered above just as brightly as any other cold winter night, but they seemed so bright and lovely to Silas at that moment.] A strange calmness came over him[, and](as) he [noticed](turned his eyes to) the man [with the hammer,] poised to strike.
Silas [simply] poked him in the belly (with his finger or maybe something more substantial?)[, and](As) [he](the rebel) hell forward[.](,) Silas gained his feet(.) [ staggering](Still staggering), [and then he saw the] (another fiend charged forward or some such)[ man] with [the](an) axe. Silas [avoided the heavy stroke, and] danced to the side, before poking [him](the blackguard) in the kidney.
The man fell as well.
* try to incorporate a thump or something
Then Silas drew his dagger in his left hand, and with his sword in his right he roared with laughter.
* Silas is a bit bloodthirsty!
[Silas](He) ran towards a small group of men[, feeling as if he were in water, he](and) was on the first one who stabbed out at him with [his](a) sword.
[For a moment Silas closed his eyes and took a deep breath.]
* no time for drama! Silas is a bloodthirsty pro!
[ Silas ducked](Ducking) to the side[ and](, Silas) drove his dagger into the man’s bicep(.) [, the](The) man shrieked and let his arm hang limp. Silas turned aside another sword, and again stabbed at a soft part.
Soon the men who fought him found themselves unable to defend against the strokes of Silas. [They](One) fell, and then two more, and then [five](another)[,](.)
Silas laughed as he danced among them, dealing death all about him. The Rebels broke for the river in a rout, as his brother finished off those that were left on this side of the river.
(For a moment,) Silas stood[ there for a moment while there were](with no foes left to fight, laughed once more, and fell.
Here is the bigger picture advice .... according to me anyways!
- I'm not sure whether you use only a few, and very long, paragraphs, or whether the site's formatting played up. If it's not the latter, you need to look at your paragraph lengths and vary it much more. A google search (site like writersdigest.com as well) will give you heaps of ideas how to address this. If it was the site, and you're doing all of this, then we're good and please ignore this one!
- Try and minimise -ing words, I'm not saying you can't use it at all (you'll notice I've actually suggested to use a few), but if you can avoid an -ing word, rather do so
- Always read your work and look for instances where you can get rid of words as far as possible, keep it short and direct as much as you can. As for the above, this is not a "you shall do this always" suggestion, but cut words that don't carry their weight and don't make an impact
- Avoid the semi-colon if you can and rather just split the semi-colon connected sentences into two separate sentences. This is probably a suggestion that falls in the always category, but if you must use semi-colons, the general rule is to use one per novel and no more. It's tricky to get it right and in general readers don't like it
- In general, rules are made to be broken. But it needs to be done for a good reason and with intent, otherwise it might come across as grammar/punctuation mistakes. As you've probably notices, I couldn't identify any reason why you'd want to do that. Personally, I've decided to leave cute party tricks like this to other authors, so I stick to grammar and punctuation rules as a rule. But if you have done it on purpose, it would still need a lot of work to bring the reason and intent for doing so across.
As I said, it may look really bad. But I hope it helps and that you realise I do have good intentions behind this review and I didn't crush your soul and now you never want to talk to me again. I know how it feels! You should've seen my first reviews .... it was way worse and I'm not kidding. Some of the very kind reviewers had to send me emails there were that many things to fix ... But I've listened and I've learned and my writing is better because of it (a little bit, I'm still a work in progress too).
So yeah, just keep on writing. It gets easier over time and the nits/suggestions also get less and less as you go on! I promise!
Cheers Janet