Who Or What Are The 2 Witnesses Of Revelation?

And I will appoint my two witnesses, and they will prophesy for 1,260 days, clothed in sackcloth.” They are “the two olive trees” and the two lampstands, and “they stand before the Lord of the earth.” Rev. 11:3-4

First, the two witnesses are revealed as the two olive trees. Who or what do the olive trees represent throughout scripture? 

Then I asked the angel, “What are these two olive trees on the right and the left of the lampstand?” Again I asked him, “What are these two olive branches beside the two gold pipes that pour out golden oil?” He replied, “Do you not know what these are?" “No, my lord,” I said. So he said, “These are the two who are anointed to serve the Lord of all the earth.” Zech. 4:11-14

Whatever these olive trees are, they represent anointed people that serve God. So perhaps Christians could fit that description. Let's see what other clues there are.

And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree; Rom. 11:17

The Gentiles are called a "wild olive tree" and physical Israel is also called an olive tree.

For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree? Rom. 11:24

Once again, Gentiles are called an "olive tree which is wild by nature" and physical Israel is called a "good olive tree." So there you have it, those are the 2 olive trees. The Gentiles and physical Israel that put there faith in Christ are the two witnesses of Revelation. The two witnesses are not two individuals that appear during the last few years just before Christ's return. Now let's break down the rest of this account.

Measure the temple
I was given a reed like a measuring rod and was told, “Go and measure the temple of God and the altar, with its worshipers. But exclude the outer court; do not measure it, because it has been given to the Gentiles. Rev. 11:1-2

Now compare the following verse to aid in the above verses interpretation.

Don’t you know that you yourselves are God’s temple and that God’s Spirit dwells in your midst? If anyone destroys God’s temple, God will destroy that person; for God’s temple is sacred, and you together are that temple. 1 Cor. 3:16-17

1260 Years
I believe that when this account talks about the 1260 years, it is referencing back in time in order to further identify who the two witnesses are.

1)They(Gentiles) will trample on the holy city for 42 months. Rev. 11:2
2)And I will appoint my two witnesses, and they will prophesy for 1,260 days, clothed in sackcloth. Rev. 11:3
3)For three and a half days some from every people, tribe, language and nation will gaze on their bodies and refuse them burial. Rev. 11:9
4)But after the three and a half days the breath of life from God entered them, and they stood on their feet, and terror struck those who saw them. Rev. 11:11

42 months = 3.5 years = 1260 days = 1260 prophetic years
1260 days = 1260 prophetic years
3.5 days = 3.5 prophetic years

Papal Rome persecuted the 2 witnesses during their reign between 538ad - 1798ad which equals 1260 years. 

The Power of the Two Witnesses
If anyone tries to harm them, fire comes from their mouths and devours their enemies. This is how anyone who wants to harm them must die. They have power to shut up the heavens so that it will not rain during the time they are prophesying; and they have power to turn the waters into blood and to strike the earth with every kind of plague as often as they want. Rev. 11:5-6