A quality bridge; granite piers, the best ship-plate steel, and a never-ending paint job..." The three main characters represent different elements of the protagonist.

Alex is a real person, born in Glasgow, who studied geology and engineering at the University of Edinburgh, fell in love with Andrea Cramond while there, and has continued their (open) relationship ever since.

He is embittered by his betrayal of his working-class roots (he has become a manager and partner in his engineering firm), the Cold War, successive Thatcher governments, and the failure of his relationship under the pressure of Andrea's French lover's terminal illness.

He finds that, in stark contrast to the very orderly, indeed totalitarian, life on The Bridge, the countryside beyond exists in militaristic chaos and warfare.

The Barbarian is an id-ish warrior with a superego-esque familiar in tow (phallic symbolism is referenced by the familiar within a few pages of their first appearance) whose hack-and slash antics through various parodies of Greek legends and fairy tales are phonetically rendered in Scots dialect (seven years before Irvine Welsh used the technique in Trainspotting).

A woman is his enemy in their first appearance (Metamorphosis, Four), showing how Andrea Cramond has made her influence felt in Alex's very core, and how his love for her has been eroded and has transmuted into anger and contempt through the rift that has opened in their relationship.

The third appearance of the Barbarian and familiar (Metamorphosis, Pliocene) sees them old, decrepit, bed-bound and heading inevitably towards death.

In each successive chapter the Barbarian's Scottish accent becomes less and less pronounced, another indication of how far Alex has gone from his Glaswegian roots.

While comparisons have been drawn between Sigmund Freud's structural theory of personality, this is the only point where the Barbarian, Familiar and another individual get together in a three-way arrangement.

In a move mirroring Alex's suicide drive and anticipating the end of the book, he is placed in a situation likely to kill him, but triumphs and emerges (literally) rejuvenated and reinvigorated.

The Bridge is an unconventional love story; the characters eschew fidelity and barely see each other for years at a time, but they keep returning to each other.

There is no marriage, no ring, no happy ever after, just the knowledge that their lives are so deeply entwined it would be difficult or impossible for them to break away from each other.

However, Banks stated "That one knife missile mention has been enough for purists to claim that, technically, The Bridge is a Culture novel.