FOLLY ARCH
Folly Arch is attributed to the architect James Gibbs (although there is no direct evidence to support this), and was part of garden designer Charles Bridgeman's plans for Jeremy Sambrooke of Gobions.
The arch is listed by Pevsner and the Historic England Grade II* listing as being built c1740. However, there is no definite way of dating the arch, and it is possible that the arch was constructed as early as the 1720s as it is known that the gardens were already well advanced in 1732 when Queen Caroline visited.
The earliest known drawing possibly predates the building of the arch.
It is taken from a map of Gobions in the Bodleian Library, Oxford, and although undated and without a title or surveyor it is possibly a design by Bridgeman himself.
The map was erroneously listed in the library catalogue as a 'Map of North Mimms Park' and was not identified as Gobions until landscape historian Anne Rowe recognised it as such c2010.
It is clear that the arch was constructed identically to this design.
It is also possible that, given the accuracy of the drawing, the arch was already built as an entrance gateway to Gobions House and later incorporated into the Bridgeman designs for the gardens as a folly.
Two large cracks appeared in the 1990s.
It was only after extensive and protracted negotiations between the NMDGBS, the owners, Borough Council and English Heritage that repairs finally commenced years later in 2003.
Underpinning the towers was prohibitively expensive. So it was decided to ensure the integrity of the towers and arch in the medium term, accepting that settlement was likely to be progressive and further remedial work to the foundations may be essential.
The arch and panel have been reinforced. Tie rods have been installed between the towers in drilled holes, plus diagonal tangential ties terminating in a reinforced concrete beam cast in the former gutter between the arch parapets.
The most eroded bricks have had extensive repointing and replacement, filling the voids left by decaying wall plates. External faces of the brickwork have been repaired and the tie cores pressure grouted with a cement grout. Reforming and supporting the jetted battlement tops, cornices and details should ensure the most exposed and inaccessible structure has been given an extended life. The work was completed in July 2003 at a total cost of £112,000 partly funded by an 88% grant from English Heritage. None of the strengthening work is visible, so it is easy to suppose that only superficial brick repairs have been carried out, which is not the case. A monitoring regime and contingency plans have been agreed with EH should further movement occur. The Building Research Establishment thought the Cedar tree close to the east tower was largely responsible for recent shrinkage of the clay subsoil, which has resulted in differential settlement of the towers leading to the distress and damage.
EH said that it is likely that future stability depends upon effective management of adjoining trees (to limit soil shrinkage) which are not under the control of the owners of Folly Lodge and Arch.
It is clear that the structural integrity of the arch will undoubtedly need further attention in the future, probably in about 50 years if the past cycles are anything to go by, and it is hoped that future generations will look after the arch as well as the past.