Blue Mountains mayor Mark Greenhill has added his voice to local residents who have condemned vandalism of the historic Knapsack Viaduct at Lapstone.
Vandals have turned the historic viaduct into an illegal canvas, scrawling motivational messages, apologies, pictures and not-so-diplomatic doodles on it.
Mayor Greenhill said the vandalism "is all the more distressing because of the historical significance of the site".
"It is a thoughtless and heartless act that denigrates our forebears. Council has a strategic approach to graffiti but sites like this are more delicate than most. The community is genuinely shocked by this event and we will do all we can to minimise the risk of it happening again," he said.
Residents who use the Lapstone Bridge Zig Zag walk - including the historic bridge - have become frustrated with graffiti vandals and their tags.
Avid walker Beth Moore said she was horrified that people would "disrespect history".
"It's an absolute marvel of construction," Ms Moore said. "It's a beautiful spot and it shouldn't be defaced. People are spoiling nature's beauty."
Georgina Williamson of Emu Plains agreed.
"I think these people should have a place and a time to do that sort of thing rather than on significant historical places," Mrs Williamson said.
"It's unfair on people who want to come up here and want to walk."
The sandstone viaduct was designed by the father of NSW railways, engineer John Whitton, and built between 1863 and 1867. The bridge later formed part of the Great Western Highway until being bypassed in the mid-1990s. It is now used by walkers, cyclists, runners and birdwatchers.
A spokesman for Roads and Maritime Services said the bridge would be inspected and arrangements would be made to remove the graffiti.
But walker and cyclist Dennis Trembath believes police should monitor the bridge regularly to stop vandalism.
"The police should swing by on Friday, Saturday and Sunday nights and see who is here," he said.
"It would take them a couple of minutes off their normal route. Once these people see the police take an interest in the area they will never turn up."