As part of the work a crane will lift and place 88 pre-cast concrete and limestone units weighing in at 10 tonnes per unit and 114 granite slabs that each weigh 12 tonnes to the west of Spur Redoubt.
There will also be 62 parapet units installed to make up the top of the wall.
The new sea defences will fit in with the historic Long Curtain Moat area, thanks to sourcing of stone to match the original seawalls, including granite from Ireland and Purbeck Limestone from Dorset.
Councillor Hugh Mason, the council’s planning boss, said: ‘This is great work from the Southsea Coastal Scheme because it strikes a delicate balance between building sturdy new defences alongside undertaking intricate work to preserve the rich historic significance of this area.
‘This scheme is going to be hugely beneficial because, without raising and strengthening the existing defences, we could well see a future Portsmouth reverting to being a morass in the wake of climate change and other factors.’
Southsea Coastal Scheme project director, Guy Mason, added: ‘The placement of the first units represents a huge milestone as it comes after more than a year of consultation with Historic England to ensure the stone used was the right fit in this heritage-protected area. In engineering terms, it's also pretty unique.
‘We're committed to working with Historic England throughout the project and will keep in close contact as we move into the next phase of the Scheme around Southsea Castle in 2022.’
The Southsea Coastal Scheme is the UK’s largest local authority-led coastal defences’ project, worth more than £100m. It will stretch for 4.5km from Old Portsmouth to Eastney.
Work at Long Curtain Moat is set to finish in autumn 2022.