This research note reports the existence of a manuscript which I first came across in the 1980s. I drew attention to it online in the hope of encouraging its further study. It has now been published as Paola Giacomoni (ed.), Jacopo Aconcio: Trattato sulle fortificazioni, Istituto Nazionale di Studi sul Rinascimento, Studi e Testi 48 (Firenze: Leo S. Olschki, 2011).

Jacopo Aconcio’s lost treatise on fortification


Jacopo Aconcio is best known as the earliest Renaissance proponent of a systematic case for religious toleration. But his interests and activities reached much more widely. In a pioneering article of 1967, Lynn White jr brought together the scattered material on Aconcio’s career as an engineer, noting that ‘while much is known of his religious activity, the present state of scholarship has permitted us only casual glimpses of his technological work and connections’ (‘Jacopo Aconcio as an Engineer’, American Historical Review, 72 (1967), 425-444, p. 425). White not only illuminated Aconcio’s origins as an engineer, but drew particular attention to his technical endeavours in Elizabethan England: as a religious refugee from Counter-Reformation Italy, Aconcio arrived in England in 1559 having initially fled to Switzerland in 1557 and latterly to France. Naturalised in 1561, he remained in England until his death in 1566 or 1567.

White’s work has been noted, but scarcely developed. The most recent biographical memoir is by Alex Keller in the Oxford Dictionary of National Biography, but the only real addition to White’s account of Aconcio as an engineer is by V. Gabrieli, ‘Aconcio in Inghilterra (1559-1566): i baluardi di Berwick e gli “Stratagemmi di Satana”’, La Cultura, 21 (1983), 309-340. White had transcribed and translated some autobiographical remarks from Aconcio’s 1564 Latin memorandum on the fortifications of Berwick-on-Tweed. Gabrieli gives a full transcription of the manuscript. As a more general indicator of the current state of play, a Google search for ‘Jacopo Aconcio’, ‘Jacobus Acontius’, ‘Giacomo Concio’ or any of the other variants of his name turns up pages on the religious toleration advocated in the Satanae stratagemata libri octo (Basel, 1565), but not much else.

One reason for the continued inattention to Aconcio’s technical career is lack of evidence. Aconcio acted as a consultant on the new Italian style of fortification while in England and, as White and others before him had noted, wrote a treatise on the subject, initially in Italian but subsequently translated into Latin. A report that this was posthumously published appears to be a bibliographic ghost, and White was unable to find the text in manuscript form.

The rediscovered volume

In this short note, I draw attention to a contemporary English version of Aconcio’s treatise. The text survives in the Petworth House Archives, MS HMC 143, and the information and transcriptions published here appear by permission of the Archives’ owner, Lord Egremont. (Access to the manuscript is supervised by the West Sussex Record Office, Chichester; see the Record Office website for general notes on the Petworth House Archives.) Although the reference appears to have gone entirely unnoticed, the manuscript was listed in Historical Manuscripts Commission, Manuscripts at Petworth House: Appendix to Sixth Report (1877), p. 313. The manuscript consists of 62 leaves interspersed with diagrams, some of which are woodcuts. The text consists of a preface followed by 48 short chapters, the first eleven of which are numbered in the manuscript.

On the flyleaf of the volume is a dedication by the translator:

xiiij Junij 1573.
To the right honourable and his singular good lord the Earl of Bedford, Thomas Blondevyle sendeth this book as a token of his good will, thankful mind and bound duty towards his Honour.

Thomas Blundeville, who issued works on horsemanship, logic and various branches of mathematics, was not only a friend of Aconcio but translated other work by him. In dedicating his The true order and Methode of wryting and reading Hystories (London, 1574) to the Earl of Leicester, Blundeville wrote that he had collected the precepts of his short text partly from the work of Francesco Patrizi and ‘partly out of a little written Treatyse, which myne olde friende of good memorie, Accontio did not many yeares since present to your Honor in the Italian tongue’ (sig Aijv).

Aconcio’s preface

In the following transcription of the preface to the volume contractions have been expanded and punctuation and spelling modernised.

[folio 1r:] The preface of Jacobus Accontius to his book of fortifying.
No man is I think so ignorant as needeth now to learn how necessary a thing it is, and specially for those that love peace and quietness, to have their dominions and towns well fortified in defence of the enemy. For who almost hath so little judgement, but that he perceives the fortifying of towns and castles to have been the chiefest cause why kingdoms have not been so easily conquered now in these out latter days, as they have been in times past. For we have seen of late towns of such strength as have been able to withstand the force of a royal army, in such sort as after long abode in besieging the same with great expense and loss of men, they have been glad to depart at length with shame enough. Some towns again do seem even at the first sight so inexpungable, as no man indeed, be he never so covetous of goods or glory, dare once attempt the same. Then, if fortifying be profitable and necessary, the true order and right way of fortifying must of necessity be also profitable. And that not only to such as profess such kind of art (to whom it is sufficient [folio 1v:] that they being accounted cunning may gain thereby and find such as will set them on work) but also to those which should bestow the cost, who otherwise perhaps being beguiled by unskilful engineers or architects, that is to say chief masters of works, may bestow all their costs in vain. Yea, and that to their own destruction as I have known some to have done in my time, which thing afterwards they have bitterly repented. This knowledge also is as necessary for such as would besiege any town as for those that have to defend the same. For being able hereby to judge and discern which towns be strong and which be not, they will neither be too rash in attempting things impossible, nor yet despair where likelihood is to attain their purpose. And finally where this knowledge is there shall be neither in besieging nor in defending any disorder ever committed. But for the most part those that exercise this art be in such an heresy as they think it almost a thing impossible to comprehend the same under any certain rules because there is so infinite diversity of sites, and that every diverse site requireth a diverse fashion of fortifying, in such sort as [folio 2r:] without very long experience a man cannot know how every site ought to be fortified. Which if it were true I would not marvel, though very few princes and chieftains would apply their minds thereunto. But as I am assured how much these men do deceive themselves in so supposing, even so I do think it no marvel at all sith that such kind of men for the most part being unlearned understand not what it is to separate particulars from universals, and the same universals aptly to divide into their parts, and to find out the nighest causes of things (which thing) though not many, yet some there be that can do it right well. For though both the words and meanings of men be infinite, yet by experience you do see that a few letters do suffice to comprehend the said words and to represent and notify them in such sort that those that be absent, yea and born of a long time after, do easily know and understand the meaning thereof. The doubtful questions also that daily do rise amongst men are infinite, yet is there invented an art whereby the truth is truly tried. The like may be said of all other things [folio 2v:] appertaining to other arts. Wherefore it followeth not that because there be so many diverse sites no art therefore can be invented under the which all such sites may be comprehended. For though there be many diverse sites indeed, yet the causes making any site strong or weak be not so many but that they may be contained in a very small volume. But to do that well, it behoveth first to have that art which teacheth the right way and method to learn all other arts; which art as I have long time laboured to attain, even so I hope my little book entitled de methodo, which I wrote to the common profit of all students, doth well testify my labour not vainly bestowed. Wherefore as one utterly rejecting the foresaid opinion of the common sort of architects, after long time spent as well in conferring with the best learned of that profession and the most skilful warriors that were then in Italy, as also in viewing diligently all such holds and forts as were worthy to be seen, I proved at length whether I could reduce the same into any art or not, the success whereof the thing itself I trust shall show. Neither have I taken upon me here to teach such an art as [folio 3r:] being but only read might suffice to make the reader by and by an architect or engineer, for that hath not been seen in any other art. Notwithstanding I believe the only reading thereof will teach him somewhat to judge of works already wrought. But to make this art known, it requireth (as all other arts do) exercise and practice, if not in making many works, yet at the least in beholding works already made, in the which you must diligently mark what is worth praise and what is not; you must also consider the first beginnings and the proceedings of the same, to the intent that you may plainly see with what order everything was wrought, for sith that in fortifying no error can be committed without great loss and peril, every man therefore than would be an engineer is not to be admitted. For as it is not enough to have the precepts and rules of this art without practising the same, even so the practice is not available without the right order and way to know wherefore and to what end every thing is done. For which cause those are greatly to be reproved for their rashness which so soon as they have seen one fort [folio 3v:] or two, and have the shape thereof in their heads, or, perchance have but learned to counterfeit a platt or two in a paper, not able to render any reason thereof, will take upon them to be engineers, to the great loss and peril of those princes or commonweals that shall hap to employ their labour. For though some one of them in making a fort or hold do follow in a certain likeness some other fort made before according to art, yet if it hap that the said fort come to be besieged of a puissant army the ignorance of the craftsman (though all too late) will then appear. Wherefore all princes and commonweals at whose great costs and charges such holds and forts are to be built, had need always to take good heed whom they admit to be their engineers.

An outline of the text

The following list of chapter headings has been extracted from the manuscript. I have supplied numbers for all except the first 11 chapters. As with the preface, contractions have been expanded and punctuation and spelling modernised.

  1. A division of fortification.
  2. What is required generally in all kinds of forts.
  3. What things do make a fort strong and able to abide the force of the enemy.
  4. What maketh forts easy to be defended.
  5. Things letting [hindering] the enemy to approach.
  6. Wherein consisteth the advantage that the defendants have in fighting with the enemy.
  7. How a fort or hold may be made to have all these foresaid commodities.
    [i] A platt form.
    [ii] What flankers every bulwark ought to have.
    [iii] The second platt form.
    [iv] The third platt form.
    [v] The fourth platt form.
    [vi] The fifth platt form.
  8. To know what commodity or discommodity every kind of site hath.
  9. What things the enemy chiefly seeketh to decay or bring to ruin for the winning of a fort or hold.
  10. How many manner of ways walls may be brought to ruin and which be the common remedies against the same.
  11. What special remedies there be against shot.
  12. How the flankers of bulwarks ought to be made.
  13. Remedies against mines.
  14. Remedies against trenching and digging down the foundations of forts.
  15. How to rememdy such mischiefs as the enemy may work against the dike environing the fort.
  16. Of the altering and changing of the site.
  17. That within the walls a large space is to be left void of building and all other encumbrances.
  18. That it is not good for a fort to be divided with many floods, brooks or channels.
  19. That the gates of a fort ought to be covered and not seen without.
  20. Of secret or covered ways.
  21. Of privy or secret gates otherwise called postern gates.
  22. How a suspected band or company may be received into a fort without danger.
  23. Of places meet to contain and keep the munition.
  24. Of the soldiers’ lodgings.
  25. How forts may be easily or hardly besieged.
  26. Of treasons and sudden attempts.
  27. What things do make a fort durable.
  28. What things do make a fort to seem fair and beautiful.
  29. Of costs and charges in fortifying.
  30. Of the matter whereof forts are made.
  31. Of the differences of sites or situations.
  32. How the defects of sites may be amended.
  33. How platt forms ought to be made.
  34. A description of a platt form made only with head corner bulwarks.
  35. A description of a platt form having one only cavalier or bastard bulwark betwixt ij head corner bulwarks.
  36. The description of a platt form having ij cavaliers or bastard bulwarks placed betwixt any ij head corner bulwarks.
  37. With what diligence the work that is to be made ought to be examined.
  38. What order is to be observed and kept in building the work.
  39. Of the slope of the wall.
  40. Of binding or anchoring the wall and other like advertisements.
  41. Of works made of turf.
  42. How old works are to be repaired.
  43. What difference there is betwixt those forts that are only made for the love of the place that is fortified and those that are made for other respects.
  44. Of the greatness and measure that is to be observed in the chief parts of a fort.
  45. That a large place to be fortified yieldeth more [ad]vantages than that which is small in circuit.
  46. That some places ought to be made strong but not over strong.
  47. A division of those forts that are made not for the place’s sake but for other respects and what is to be considered in every one of them.
  48. Of forts that be severally made by themselves for other respects than for the place’s sake.


Aconcio’s treatise contains much detail that would repay further comparative study. Yet despite the discussion of practical matters such as materials, construction techniques and the inclination of walls, the text is somewhat bloodless. This is in part because Aconcio was more an observer of fortification than an engineer formed through long experience of construction, campaigns and sieges. But it is also because, in playing to his own strengths and seeking to carve out a niche for himself as an engineering consultant, he presented the art as a self-conscious exemplification of ‘method’, the general logical technique for resolving questions presented in his De methodo, hoc est, de recta investigandarum tradendarumque scientiarum ratione (Basel, 1558).

In accordance with his explicit aim of reaching general rules amidst the infinite particularities and circumstances of fortification, Aconcio scarcely mentions individual places. Milan appears twice (10v and 18r) and ‘the Cite of Auguste in almanie hathe no needed to be fortefied, but for yt sellfes sake, sithe the Citezens therof have withowt the walls no territories nor domynion at all’ (3v - 4r). Aconcio is equally reticent in citing literary sources. Only Vitruvius is repeatedly mentioned and there are a couple of references to ‘palladius’ (36r-v). If the latter refer to Andrea Palladio, whose Four Books on Architecture appeared in 1570, then they were presumably inserted by Blundeville.

The methodical and discursive nature of the text reveals one of the few points where Lynn White’s otherwise sure-footed characterisation of Aconcio needs to be qualified. White wrote that ‘the essence of the new mode of fortification was the application of mathematics to its problems, and Aconcio’s mental process was permeated by the mathematical method of starting from clear and concrete principles, and passing step by step to greater generality and simplicity’ (White, p. 426). While it is true that the new angle bastion style of fortification was very often presented as a mathematical art, the discovery of Aconcio’s treatise shows that he was not a strong advocate of what would become the conventional approach. He makes no appeal to geometry; rather, it is his own ‘method’ that provides the overarching framework for analysis. Aconcio’s treatise should therefore be critically compared with the contemporary mathematical literature of fortification. This may prove to be the most significant dimension of his work: he provides a counter-text against which the values, agenda and, indeed, silences of the more conventional handbooks will be clearly revealed.

Note: Aconcio in Latin

As long ago as the mid-19th century, it was recognised that Aconcio had first written on fortification in Italian before making a Latin translation available. In book VIII of the Stratagematum Satanae, there is a letter from Aconcio to John Wolf dated 21 December 1562, in which he refers to the translation of his long-completed Italian work into Latin under the title Ars muniendorum oppidorum. (Carlo Promis, Dell’Arte dell’Ingegnere e Dell’Artigliere in Italia dalla sua origine sino al principio del XVI secolo. Memorie Storici (Turin, 1841), pp. 91-2.)

Although no copies of either the Italian or Latin versions have been found, Aconcio himself says that he circulated at least the latter when he first came to England (White, p. 443). Lynn White speculated that Lord Burghley would have had a copy, and this can be confirmed. A Latin version turned up in a late 17th-century book sale which comprised ‘the main part of the Library of that Famous Secretary William Cecil, Lord Burleigh’ (preface to T. Bentley and B. Walford, Bibliotheca Illustris: sive Catalogus Variorum Librorum ... Quorum Auctis habebitur Londini, ad Insigne Ursi in Vico dicto Ave-Mary-Lane prope Templum D. Pauli, Novemb. 21 1687 (London, 1687)). Number 109 of the ‘Manuscripti Latini, in Quarto’ is ‘Jacobus Acontius de Oppidis Arcibusque muniendis’ (p. 86). The British Library copy of the catalogue (shelfmark 821.i.8.(1.)) is signed on the title page ‘A Palmer -87’ and contains the prices marked against many of the items. Aconcio’s text sold for 2 shillings.