Did Nostradamus predict 9/11?
In the heightened days following September 11, 2001 there were a lot of reports that Nostradamus had predicted the terrorist attacks on the World Trade Center in New York!

You may have even read about the quatrain below:

In the City of God there will be a great thunder,
Two brothers torn apart by Chaos, while the fortress endures,
the great leader will succumb,
The third big war will begin when the big city is burning.

First off, let's say straight out that this was not written by Nostradamus at all. Yes it superficially resembles his style, but there is no such quatrain and he didn't write it. In fact, some sites that reference this verse state it was written in 1654 which would be an impressive feat for someone who died nearly 100 years before!

Before we look at who did write it, let us use it as an exercise in critical thinking. We will break down the key points it raises:

City of God. This could match anything you like - Mecca, or a city with a lot of churches (e.g. Rome), or a city with many religions (e.g. Jerusalem), or a city which is unusually impressive. You name it. 
Two brothers torn apart by chaos. Again this could be anything. Allied countries, or political party coalitions, or two ajoining neighborhoods, or royalty where there have been numerous inter marriages. etc. 
The third big war. Give me a break. How many big wars have there been since Nostradamus was alive? Even excluding WW I & II, you should immediately think of Vietnam, the Gulf War, the US Civil War, the Napoleonic wars, the Crimea, the Russian Civil War, the Russia-Japan war, the American War of Independence, the Spanish Civil War. And so on. Tens if not hundreds of thousands died in each these conflicts. Is that not big enough? 
A big city burning.. Tends to happen in wars. Dozens alone in World War II - Dresden, London, Berlin, Stalingrad, Hiroshima, Nagasaki, Tokyo. 
When all is considered we are left with is a verse which is so ambiguous on every line that you could with little effort match it to many different possibilities.

So who wrote this quatrain and what was their point?

This quatrain was actually created by a student called Neil Marshall in an article called "A Critical Analysis of Nostradamus". His point in writing the above was to highlight that some Nostradamus quatrains are so vague as to be open to any interpretation after the fact.

"1. THE MAN FROM THE EAST AT HOME IN THE WEST
He will appear in Asia (and be) at home in Europe . . . C 10 Q 75
The man from the East will come out of his seat
Passing across the Apennines to see France
He will fly through the sky . . . C 2 Q 29

2. Great HERME'S ROD
He will fly through the sky, the rains and the snows
And strike everyone with his rod C 2 Q 29
He will appear in Asia, at home in Europe.
One who is issued from the great Hermes . . . C 10 Q 75

In two major quatrains about a man from the East there are allusions to the iron rod of Hermes. This rod is often interpreted in terms of a nuclear missile, a reading which makes the man an agent of the Antichrist. But interpreters should also remember the occult significance of Nostradamus' choice of vocabulary. The Hermes reference links the rod to the caduceus wand, the Western symbol for enlightenment. The rod has the power to transform, liberating the individual to the truth. This man from the east wields the rod like a Zen stick to jolt the world into waking from its illusions. From this, we can infer that Nostradamus is describing an Eastern teacher who strikes at the world and would, therefore, be unpopular. He might use unusual and unorthodox devices to stir people up, disturbing the status "codes" of social and religious behavior in our materialistic times.

3. THE OUTLAW TEACHER
A man will be charged with destroying the temple and religions altered by fantasy.
He will harm the rocks rather than the living.
Ears filled with ornate speeches. C 1 Q 96

The idea that old religion is a fantasy or a shadow of its living teaching is a recurring theme. The man mentioned in Century 1, Quatrain 96 will strike out against traditional rock-like dogmas, earning the unified wrath of the world's organized religions.

4. THE MYSTIC ROSE
Against the red ones religions will unite . . . C 9 Q 51
(Those who plot are at point of dying
Except one who above all will run the world. C 9 Q 51.)
The rose (color) upon the middle of the world scene . . .
To speak the truth they will have closed mouths.
Then at the time of need the awaited one will come late. C 5 Q 96

Most interpreters of Nostradamus believe that his references to the color red relate to revolutionaries. But perhaps these revolutionaries are not those from Russia or France which spring most readily to mind. Red or shades of "rose" are colors used symbolically by Eastern mystics and seekers to represent the fire of awareness, the sunset of the old world and the dawning of the inner enlightenment, described by spiritual traditions as "The Mystic Rose." A riddle "to speak with closed mouths" is almost a Zen koan, and may very well describe the 1990's worldwide interest in Eastern meditation techniques. In fact, there is more mainstream interest in meditation in these latter-days of the 20th century than there was during the revolutionary 1960s.

5. MARS AND THE FLAME
. . . at the eve of another desolation
When the perverted church is atop her most high and sublime dignity . . .,
There will proceed one born from a branch long barren,
Who will deliver the people of the world from a meek and voluntary slavery
And place them under the protection of Mars . . .
The flame of a sect shall spread the world over . . . Epistle to Henry II

Here Nostradamus attempts to describe what is the cornerstone of all major religions — the concept of complete surrender to belief. His poetic references to liberating individuals from the "voluntary slavery" of belief, a tenet of faith historically abused by religious leaders to keep people obedient, becomes less clear in the last line of the quoted section from Nostradamus' Epistle to Henry II: "place them under the protection of Mars."But is we look at the occult connection between Mars in its higher form and Hermes, the bearer of the enlightened rod, the meaning is less obscure. Mars rules the astrological sign, Aries, a fire sign, and both are represented by the color red. Eastern mystics wear red or orange, for similar symbolic reasons, as described in clue four. Higher Mars is represented by the Hermes the Magician holding the caduceus rod of enlightenment. The philosophical similarities between Hermetic teachings and Eastern tantra, the main essence of Eastern philosophies, seem to imply that this new religion is not like the old, judgmental faiths, but perhaps teaches a new acceptance of life. This teaching would certainly be in tune with modern developments towards change through the "Human Potential" movement — a kind of magic used as a launch pad to an experience of the divine.

6. DIANA (THE MOON) AND DHYAN
Sooner or later you will see great changes, extreme horrors and vengeance,
For the moon is led by its angel,
The heavens approach the Balance.
(Astrological — Pluto transit of Libra 1972-1984) 

C1 Q 56

The great amount of silver of Diana (moon) and Mercury (Hermes.)
The images will be seen in the lake (the mind of meditation)
The sculptor looking for new clay.
He and his followers will be soaked in gold.
(a Hermetic reference to the attainment of enlightenment.) 

C 9 Q 12

Second to the last of the prophet's name
Will take Diana's day (the moon's day) as his day of rest . . . 

C 2 Q 28

The moon in the middle of the night . . .The young sage alone with his mind has seen it.
His disciples invite him to become immortal . . .
His body in the fire.

C 4 Q 31

The allusions to "silent rest," "images," . . . seen" and "alone with his mind" imply the silence and distance from thought experienced by the individual who, in a state of meditation, observes the changeability of life, the mind, and the emotions. Buddha called meditation Dhyana or Dhyan, a name which corresponds to the French pronouncement of "Diana" used by Nostradamus. Here again, therefore, fire and Hermes are linked. The references in the first line of Quatrain 28 Century 2 also seem to infer that the new spiritual leader has a name related to the moon.

7. THE INFURIATING TRAVELER
. . . (he) will take Diana's day as his day of silent rest.
He will travel far and wide in his drive to infuriate,
Delivering a great people from subjection. 

C 2 Q 28

Clue 5 also refers to a "people" linked to Hermes, the moon and meditation and the coming to the West of an eastern teacher. Perhaps the teacher travels, or will travel, around the world. Maybe the controversial message of his "drive to infuriate" orthodox belief will keep the teacher on the move. Nostradamus implies that he will only rest on Diana's day, which would be Monday, the moon's day.

8. THE RARE BIRD CRIES "NOW!"
. . . the Antichrist returns for the last time . . . All the Christian and infidel nations will tremble . . . for the space of twenty-five years. Wars and battles will be more grievous than ever. Towns, cities, citadels and other structures will be destroyed . . . So many evils by Satan's prince will be committed that almost the entire world will find itself undone and desolated. Before these events many rare birds will cry in the air. "Now!" "Now!" and sometimes later will vanish. (Epistle to Henry II)

Nostradamus is fond of using riddles about animal life, such as the swarms of bees and the eagle used to describe Napoleon’s crest of arms. The birds in this part of the Epistle to Henry II may be another riddle, perhaps a symbol relating to some aspect of the religious visionary who will help ward off the dire apocalyptic events described in the rest of the passage. The message may be anti-prophetic in that the key to avert disaster may come from abandoning both the past and our obsession with tomorrow. Instead, we should focus all our intelligence and energy on "Now!" The rod or the Zen stick only "strikes" in the present moment. According to Eastern mystics enlightenment is ever "now." "

"Madam Blavatsky, one of the leading psychic seers of the 19th century, predicted that the Maitreya would appear in Asia around the year 1950. "We are at the close of the cycle of five thousand years of the present Aryan Kali Yuga, or Dark Age. This will be succeeded by the age of light . . . A new messenger of the spirit will be sent to the western nations. He is appearing in 1975." . . .

Nostradamus' equivalent to Blavatsky's prophecy occurs in Century 4, Quatrain 50.

Libra will see the western lands (America) to govern,
Holding the rule over the skies and the earth
No one will see the forces of Asia destroyed
Until seven hold the hierarchy in succession.

C 4 Q 50
The quatrain number may imply 1950 and the superpower America, represented by Libra's scale of democracy. Here again is the reference to Middle and/or far Eastern alliances being destroyed, clearing placing this event in our new future. America is portrayed in many prophetic traditions as the most fertile ground for the new religious teachings. The "seven" are the seven millennia in Nostradamus' calculations which end in A.D. 2000, which also links this quatrain to the quatrain below:
The year the great seventh number is accomplished
Appearing at the time of the games of slaughter,
Not far from the age of the great millennium (2000)
When the dead will come out of their graves. 

C 10 Q 74
If, before the year 2000, man can reject political power games in favor of a new awakening, the world may survive into the next millennium. . . . For our last quotation in this chapter it is thus appropriate to remind ourselves of the following quatrain describing the new spiritual teacher from the East, the man we are in danger of missing.

Long awaited he will never return.
He will appear in Asia (and be) at home in Europe,
One who is issued from the great Hermes . . . 

C 10 Q 75
We are still not far enough down the line to draw precise conclusions as to the identity of the man or men whom Nostradamus and many other prophets saw as the instruments of the birth of the new religion. As the prophecies unfold into reality, it remains to be seen just what we can hope to enjoy or suffer in the coming "New Age." . . .

Mars and the scepter will be in conjunction, (June 21st, 2002)
A calamitous war under Cancer. (July 1999)
A short time afterward a new king will be anointed
Who will bring peace to the earth for a very long time. 

C 6 Q24
There will be peace, union and change,
Estates and offices (that were) low, (are) high those high, (made) very low.
To prepare for a journey torments the first (child).
War to cease, civil processes, debates. 

C 9 Q 66
The first quatrain may be a promise of redemption for the world after the terrible natural disaster or war that brings terror down from the skies in July of 1999 (calamitous war in Cancer). The next time Jupiter (scepter) conjuncts Mars will be on 21 June 2002. The new king could be the long awaited Christian Messiah, or the Messiah of a half-dozen other religious traditions, who triggers Nostradamus’ promised millennium of peace on earth. The second quatrain could represent any post-cataclysmic or post war period. An occult interpretation of the third lines identifies the "first" as the children of a new mankind who are about to embark on a new era of exploration of space and the inner exploration of the soul."