Please briefly describe what battle was going on at the beginning of William Shakespeare's Macbeth, including Macbeth's role in it. 

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Lori Steinbach eNotes educator| Certified Educator

We get the same report about the nearby battle as Scotland's King Duncan in Act I scene ii of William Shakespeare's Macbeth. (Remember that Elizabethan stages were too small for any grand battle, so they had to be talked about and reported rather than enacted. This reporting of grand events is a common technique used by Shakespeare.) At first, reports the messenger, the battle was evenly matched,

As two spent swimmers, that do cling together
And choke their art.

But soon the attacking Norwegian army, led by two Scottish traitors (the "merciless Macdonwald" and the Thane of Cowdor), is defeated. The messenger reports that the King's man, Macbeth, conducted himself with great valor during this battle.

For brave Macbeth--well he deserves that name--
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valour's minion carved out his passage
Till he faced the slave;
Which ne'er shook hands, nor bade farewell to him,
Till he unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements.

Macbeth fought his way through many soldiers until he got to Macdonwald and promptly cut him open from belly to neck; then he cut off his head and placed it on a spike upon the castle walls as a punishment for treason and an inspiration to his fellow soldiers.

Though the tide of battle seemed to have turned, the Norwegian general 

surveying vantage,
With furbish'd arms and new supplies of men
Began a fresh assault.

Things do not look good for the Scots, but Macbeth and Banquo

As cannons overcharged with double cracks, so they
Doubly redoubled strokes upon the foe,

It was a fierce and bloody battle, reports the messenger; but, 

to conclude,
The victory fell on us.

For his brave and loyal actions, King Duncan will reward Macbeth with the title of "that most disloyal traitor / the thane of Cawdor" as he orders Cowdor to be hung for his traitorous acts. This will prove to be an ironic and fatal act for King Duncan.