As St Paul's finally said: march up (5)

I believe the answer is:

domed

I'm a little stuck... Click here to teach me more about this clue!

'as st paul's' is the definition.
I can't judge whether this definition defines the answer.

'finally said march up' is the wordplay.
'finally' suggests the final letters.
'march' becomes 'demo' (as in a demonstration).
'up' is a reversal indicator (in down clue: letters go upwards).
The final letter of 'said' is 'd'.
'demo' in reverse letter order is 'omed'.
'd'+'omed'='DOMED'

Can you help me to learn more?

(Other definitions for domed that I've seen before include "not flat!" , "cupola" , "with a meniscus" , "Shaped like rounded roof" , "Vaulted" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.