So restless Cromwell could not cease
In the inglorious arts of peace,
But through advent'rous war
Urged his active star:
And, like the three-forked lightning, first
Breaking the clouds where it was nursed,
Did thorough his own side
His fiery way divide.
For 'tis all one to courage high,
The emulous or enemy;
And with such, to enclose
Is more than to oppose.
Then burning through the air he went,
And palaces and temples rent;
And Caesar's head at last
Did through his laurels blast.
'Tis madness to resist or blame
The force of angry Heaven's flame;
And, if we would speak true,
Cromwell is described as a meteor hurtling through the air, destroying anything in its way. Interestingly, his destruction damages both royalty ( palaces ) and religion ( temples ), Cromwell is forging an entirely new era without the hindrances of the past. 
 “Ceasar’s head” could be a reference to the execution of Charles I. Marvell mentions how his head blasts trough his laurels which belittles his achievements as a king. 
 Alternatively, it was believed that lightning was not able to strike a laurel tree. Cromwell, represented by lightning, is able to blast the kings laurels, revealing his phenomenal power. 
 However, “Ceasar’s head” may represent Cromwell, in which case, he has the power to forcefully take the kings crown and rule.
An Horatian Ode Upon Cromwells Return from Ireland