A wall beside a historic bridge in Bath that was struck by a lorry that rolled backwards will take "months to repair".
Masonry from close to Pulteney Bridge was thrown into the River Avon after the crash on Thursday just after 16:00 GMT.
Councillor Joanna Wright, from Bath and North East Somerset (Banes), said the lorry "broke" the balustrade and its owner then "left the scene".
She said police were investigating "the vehicle that created this problem".
Pulteney Bridge is Grade 1 listed and, built in 1774, it crosses the River Avon in the city centre.
Since the damage, safety barriers have been installed and the bridge remains open to buses, taxis, cyclists and pedestrians.
Ms Wright said the "huge section that collapsed into the weir" would have to be located and "put back into place".
She added the cost of repairs would be "significant and take months" to complete.
Joanna Wright said: "It's a Unesco World Heritage site. Bath needs to be looking at its best at all times because this is a prime spot for many tourists around the world to come and see this city.
"They all like to have their photographs taken - literally where that balustrade has disappeared - and we've got to make sure it looks top notch."
Avon and Somerset Police said "officers were making inquiries to establish whether any offences have been committed".