Romeo and Juliet - Prologue
"Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life;
Whose misadventured piteous overthrows
Doth with their death bury their parents' strife.
The fearful passage of their death-mark'd love,
And the continuance of their parents' rage,
Which, but their children's end, nought could remove,
Is now the two hours' traffic of our stage;
The which if you with patient ears attend,
What here shall miss, our toil shall strive to mend."

What is the subject of "Doth with their death bury their parents' strife"? If the subject is "overthrows", shouldn't be "do" instead of "doth"?

Question

Romeo and Juliet - Prologue
"Two households, both alike in dignity,
 In fair Verona, where we lay our scene,
 From ancient grudge break to new mutiny,
 Where civil blood makes civil hands unclean.
 From forth the fatal loins of these two foes
 A pair of star-cross'd lovers take their life;
 Whose misadventured piteous overthrows
 Doth with their death bury their parents' strife.
 The fearful passage of their death-mark'd love,
 And the continuance of their parents' rage,
 Which, but their children's end, nought could remove,
 Is now the two hours' traffic of our stage;
 The which if you with patient ears attend,
 What here shall miss, our toil shall strive to mend."

What is the subject of "Doth with their death bury their parents' strife"? If the subject is "overthrows", shouldn't be "do" instead of "doth"?

Answer

jenisson,

What is the subject of "Doth with their death bury their parents' strife"? If the subject is "overthrows", shouldn't be "do" instead of "doth"?

Overthrows... is the subject.
Overthrows...means ruins or destructions.

Usually a plural subject would take a plural verb, but in this case Shakespeare is thinking of the destructions of the lovers as a single connected event and thus uses the singular verb.

He could have used the singular form of overthrows but he decided to use the plural "overthrows" to make a rhyme with the word "foes" at the end of a previous line. 
.

Answer

The subject is 'overthrows' as you mentioned.
'doth' is the archaic 'does' ,it is in the 3rd personal singular present tense of 'do'.
'overthrows' is the plural form of the noun 'overthrow' ,it is applied as  a plural noun ,thus you use the third personal singular conjugation with it 'does' ,which is the archaic 'doth'.

Answer

The subject is the "the pair of star-crossed lovers". I.e. Romeo and Juliet.