Caesar Writhes at the Shah's Letter

From D13.10, Caesar Answers Anooshirvan. It illustrates D13.10.3–14 (to D13.10.21):

D13.10.3
When Caesar read the royal letter through,He writhed in anger at the threats he knew.
D13.10.4
His brow grew wrinkled and his face turned pale,At every threat contained within the tale.
D13.10.5
He called a scribe to take down his reply,With pride and anger blazing in his eye.
D13.10.6
With ink as black as pitch, the scribe beganBy praising God, who rules the life of man:
D13.10.7
“The Artist of the heavens, Lord of all,The source of war and peace and friendship’s call,
D13.10.8
Crowns one a king and grants him high command,While one stands girt for service at his hand.
D13.10.9
Though turning heaven knelt at your behest,And Jupiter your mastery confessed,
D13.10.10
Search every record: never has Rum’s sonPaid tribute to the Kayan kings, not one.
D13.10.11
Though you are king, I am no less than you;I too have crown and troops to serve me true.
D13.10.12
Why should I bear such insults out of fearOf tuskers, tabiras that shake the ear?
D13.10.13
I now demand the tribute that you owe;Who dares confront Rum’s legions, blow for blow?
D13.10.14
You know Iskandar’s deeds across your land;That noble king was ours, with sword in hand.