At once > Immediately; together, simultaneously

3 With strokes of mortal steel without remorse,

remorse > {Compunction; mitigation; also: biting or cutting force (SUFQ; cf. 402.15:3)}

4 And on his shield like iron sledges beat:

sledges > sledge-hammers

5 As when a bear and tiger, being met 6 In cruel fight on Libyan ocean wide,

ocean > {A great expanse of anything; hence: desert}

7 Espy a traveller with feet surbated,

surbated > bruised, sore (from too much walking)

8 Whom they in equal prey hope to divide, 9 They stint their strife, and him assail on every side.