Last edited 31 Dec 2020

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John Peter Desmaretz

This article is part of ICE's Engineer biographies series.

DESMARETZ, John Peter (c.1686 - 1768), military engineer. Desmaretz's 60 year career was evenly divided between mapping and fortifying most of the coast of south-east England, eventually leading to his proposals for the harbours at Ramsgate and Shoreham, which are his main civil engineering contributions. At one period (1758) he was at the same time Clerk to the Fortifications (£60p.a.), Architect to the Ordnance Board (£120p.a.) and Master Draughtsman (£100p.a.), but his engineering training and priorities are impossible to determine as nothing is known of his life before he took service with the Duke of Marlborough in 1709.

A Huguenot background can be postulated. His epitaph tantalisingly states 'though born a foreigner he early adopted every sentiment of civil and religious liberty and exerted his active abilities for the service of this nation in quality of an engineer'.

Desmaretz stayed on after the end of the war in 1713 working with John Armstrong on the demolitions at Dunkirk where he was employed to survey the works and chart the coast between Ostend and Gravelines. His first work in England was also as a surveyor, charting the river Medway in 1724.

He was first employed by the Ordnance Board as a draftsman in the Tower in 1725, where he helped to train the next generation of military draftsmen, such as the Durnfords, Andrew Frazer and William Twiss. Despite being officially based in the Tower he still provided charts, reports and estimates and was involved in the construction of every major Board of Ordnance project in the south of England.

These included Landguard where he surveyed Harwich Harbour (1732), the Brompton Lines (1755) built to defend the dockyard at Chatham, Dover Castle (1756) where he made the first major alterations to the castle's defences in 500 years, employing 734 men and spending £3,658, and the Gosport Lines (1757) built to defend Priddy's Hard and the dockyard at Portsmouth where a large part of his career was spent, becoming overseer in 1748 and Commanding Engineer 20 years later. He drew up numerous plans of the harbour, town, dockyard and defences, one of the last (1762) with an estimate of £1,761 for repairs to the harbour for damage caused by extraordinary tides and winds.

His major work there was the design and construction of Fort Cumberland, an irregular star-shaped fort, built to defend Langstone harbour. Desmaretz's estimate of £3,787 was agreed on 18 November 1746 and work began the following new year's day. His contradictory instructions were 'to see that everything is done in a frugal but substantial manner with the best materials and all convenient dispatch'. The earthworks alone cost £1,874 involving the removal o f 52,000 cu. yd. of earth.

In 1749, while still employed on Fort Cumberland, Desmaretz seems to have answered an advertisement by the Board o f Trustees for Ramsgate for engineers to deliver sealed plans for piers of stone or wood to enlarge the harbour. He attended a meeting to give his opinion on the manner and materials for the building of these piers, and was recalled for a second meeting on the 15 December for taking into consideration all the plans and proposals.

In February 1750, work began, the overall plan of the harbour being only slightly modified from the original prepared by Edward Gatton, of the Ordnance Board, in March 1749.

By 1754, the piers had been built to about one-third of their final length when William Ockenden, one of the harbour Trustees, advocated reducing the width by 286 ft to 1,200 ft. Work on this revised plan actually started, but so annoyed local merchants and seafarers that in February 1755 the House of Commons was petitioned to put a stop to it. After a vast amount of evidence had been heard, Desmaretz and Admiral Sir Peircy Brett were commissioned to report. They proposed to retain the original width but to extend the piers into deeper water than originally intended.

For the better protection of ships liable to be damaged by lying aground they also suggested a deepened basin on the east side of the harbour. The total estimate for the works was £195,906 7s 6d. Their report of December 1755, was accepted by Parliament in February 1756, when the works done for contracting the harbour width were ordered to be taken up. Work eventually resumed in 1761 but when the piers were completed by Thomas Preston in 1772 they were very much along the original 1750 lines.

Having acquired a taste for harbour engineering Desmaretz had also been commissioned to survey Shoreham in 1753 and provide a scheme for a new entrance to the harbour, since the mouth of the river had shifted 4 miles to the east of the old village of Shoreham and was blocked with shingle. At the first meeting of the Harbour Commissioners in ' The Star' at Shoreham on 25 June 1760 it was ordered 'that a cut be made through the beach at the place fixed by a plan made by Mr Desmaretz ... and piers erected and built in order to make a useful harbour at the said town'.

This was done, and for the first few years the harbour was successful, witnesses stating 'that while the piers remained the harbour was safe and good having ... between 24 and 25 ft. depth' and that 'there was no bar or lodgements at the mouth of the harbour'.

Unfortunately, unscrupulous contractors had only driven half the piles into the marl and chalk foundations, the rest being cut off at 8 ft. and the timber sold. Unsurprisingly, the piers failed and the harbour mouth drifted back east again. When work began on restoring the harbour in 1817 the entrance was again made at the same location as Desmaretz had proposed in 1753. This time, with William Chapman as engineer and William Clegram as resident engineer, the works were properly carried out and proved entirely successful.

Desmaretz's prolific military career continued with a report and estimates for Senegal (1758), and in 1759 the building of sea defences on sites on the south coast most vulnerable to French attack from Littlehampton to Folkestone, completed in 1761 at a combined cost o f £14,764. The scale of these works, involving the use of 120,000 'exceedingly well burnt bricks' at Brighton alone, caused a shortage of bricks and timber along the entire coast.

He also worked on most of the Board of Ordnance powder mills and stores, beginning in 1733 with a porch for the west front of the magazine at Greenwich. In 1743 he reported on repairs to the gunpowder store at Woolwich and obviously by now considered an expert, worked on a project for a powder magazine in Jamaica. In 1755 he produced a report and estimates for the grand magazine at Purfleet and in 1762 - 1763 designed both horse mills and powder mills at Faversham; the same year h e also produced reports and estimates for an infirmary at Sheerness.

In 1763, Dunkirk once again came into British possession and Desmaretz returned as First Commissary and along with Andrew Frazer and William Roy drew up plans for the two new channels at Mardyke in 1766. He died there in 1768, but was buried alongside his wife in the garrison church in Portsmouth where the tablet erected by his daughter Mary luckily survived the firebombing in 1941. Mary was married to Stillingfleet Durnford who worked for the civil branch of the Ordnance as Clerk of Deliveries from 1758-1768, and had a son Desmaretz Durnford who served as an engineer in America, and a daughter Charlotte who married his former assistant at Dunkirk, Andrew Frazer.

Their son Sir Augustus Simon commanded Wellington's Horse Artillery in the Peninsular War, also continuing a family tradition, since Desmaretz himself, although never holding military rank in the Corps of Engineers had been made a Lieutenant-Colonel of Artillery in 1761.


  • 1755: A Plan for Making a Harbour at Ramsgate, jointly with Sir Peircy Brett
  • 1755: Report and Estimate Subjoined, Relating to the Harbour of Ramsgate, jointly with Sir Peircy Brett.


  • 1747 - 1750: Fort Cumberland, estimate £3,787
  • 1753: Plan for new entrance to Shoreham Harbour.
  • 1755 - 1763: Powder and horse mills at Faversham
  • 1759: Batteries on coast of Sussex and Kent, £15,000.

Written by SUSAN HOTS.

This text is an extract from A Biographical Dictionary of Civil Engineers in Great Britain and Ireland, published by ICE in 2002. Beginning with what little is known of the lives of engineers such as John Trew who practised in the Tudor period, the background, training and achievements of engineers over the following 250 years are described by specialist authors, many of whom have spent a lifetime researching the history of civil engineering.

--The Institution of Civil Engineers

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