Get out the microscope, because we’re going through this poem line-by-line.
O harp and altar, of the fury fused,
(How could mere toil align thy choiring strings!)
- Crane invokes the spirit of the bridge: "O harp and altar." This "O" is common in odes by poets like the Romantic John Keats.
- The harp or lyre is a symbol of poetry from Ancient Greece and also for the British Romantics in the 19th century (Keats again).
- The cables in the bridge look like harp strings.
- An altar is a raised platform for religious ceremonies.
- The platform of the bridge looks like an altar.
- The bridge is a symbol of both poetry (and art) and religion. These two attributes are "fused" by "fury," which can mean passion, violence, or anger.
- The Furies in Ancient Greek legend are goddesses, three sisters who represented vengeance and justice.
- The speaker thinks that "fury" must have made the bridge, because hard labor ("mere toil") could certainly not have made such a magnificent object. (Although of course it did.)
- The cables, or "strings," of the bridge/instrument are "choiring" – they seem to be in visual harmony. This returns to the idea of the bridge as a harp.
Terrific threshold of the prophet's pledge,
Prayer of pariah, and the lover's cry,--
- The bridge-as-religious-symbol theme continues
- The bridge is a "threshold" or entrance.
- It is "terrific" both in the sense of fantastic and of inspiring terror – religious terror like Moses in front of the Burning Bush.
- The bridge promises the revelation of some mystic truth, just like the pledge made by a prophet.
- The bridge is also, in a sense, the fulfillment of pledges made by past prophets. It looks like one of the fantastic images from the Book of Revelation, for example.
- Turn back to Stanza 3, where the movies were compared to a prophecy (though a dead-end one).
- The bridge is also like the response to the prayer of a pariah, someone who has been cast out of society, or the cry of a passionate lover.
- This line might refer to Crane's homosexuality. Gay people were still social pariahs in his time. The "prayer" and "cry" could be Crane's own.