Nico's 'The Marble Index' (Elektra, 1968)

According to the story, Nico's The Marble Index was the only music the American singer-songwriter, Elliott Smith listened to in the months before his violent death.

I find your albums really good to listen to late at night. What is your perfect 2.45am album?

(Smith) There are several. I think ‘Marquee Moon’ by Television and ‘The Marble Index’ by Nico (laughs).
— Interview with Elliott Smith, 'There has to be darkness in my songs' NME, March 2000

Released in 1968, Nico's The Marble Index - produced by John Cale - was a commercial failure and led to Nico being dropped by Elektra, but has since been recognised as an album of genius. Critics tend to use negative adjectives to describe it (desolate, frightening); at times even mocking it for its strange 'suicidal' mood, and yet what strikes me is the strength of the music, as embodied by Nico's voice. 

Nico's voice is at once highly individual, but also operates as just another instrument, merging with the broader soundscape (that is reminiscent of Cage, with its random recurring elements, or contemporary electronic music), see here the first track in particular, 'Lawns of Dawns'.

Her music seems both modern and ancient. Richard Watts writes that Nico's melodies are often modal, with a flattened sixth or seventh as you find in Plainchant, or folk and medieval music. 

My melodies are from the Middle Ages,’ Nico told a journalist. ‘They are from my Russian soul. I do not mean this literally, but they are that in my imagination. John Cale said that they are not tonal. They do not come from our key system. They are too old in their arrangement.
— Nico: The life and lies of an icon, Richard Watts (Virgin Publishing, 1993)

 The album only lasts a little over 30 minutes, but within that time Nico evokes an imaginary space - with mythic overtones - that is also extremely intimate. 

One of the saddest stories among the many from Nico's life relates to her son, Ari; heavily addicted to heroin, she returned to visit him (at the home of Alain Delon's parents, who raised him, near Paris) and brought him an apple as a gift, completely unaware that this might not be an appropriate present for a child.

Ari is present in Nico's music: singing the French folk-song 'Le Petit Chevalier' on her album, Desertshore (1970) and also being sung to in the kind of lullaby on 'Ari's Song' on The Marble Index

Sail away, sail away my little boy
Let the wind fill your heart with light and joy
Sail away my little boy
Let the rain wash away your cloudy days
Sail away into a dream
Let the wind send you a fantasy
Of the ancient silver sea
Now you see that only dreams
Can send you where you want to be
Now you find those faces
Are not holding places
Where you thought they’d be
And later as you go again
You will agree
That it was all a dream
Sail away, sail away my little boy
Let the wind fill your heart with light and joy
Sail away my little boy

Here Nico sings about escape, but also urges her son to understand that 'those places are not hiding places' - and it is in this ambiguous moment that you can hear her voice open, with an expression of great feeling.

Motherhood is a recurring theme in Nico's work, perhaps most notably in the song that was played at her funeral, Mutterlein from Desertshore that was written in memory of her mother. 

On the cover of Desertshore, you see a still from a Philippe Garrel film, with the child Ari leading his mother on a white horse (according to Richard Watts the little boy isn't Ari) walking with such confidence and assurance: when you remember the tragedy of his life, this image strikes me as monumentally sad.

The reissue from Rhino of these two albums, Frozen Borderline from 2009, takes its title from a line in 'Frozen Warnings' and includes a magical version of the track with Nico where she is accompanied only by viola. It is quite lovely.