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Isidorus of Miletus

Isidorus of Miletus

(b. Miletus; fl. Constantinople, sixth century)

architecture, mathematics.

Isidorus of Miletus was associated with Anthemius of Tralles (a neighboring town of Asia Minor) in the construction of the church of Hagia Sophia at Constantinople. The church begun by Constantine was destroyed in the Nika sedition on 15 January 532.1 Justinian immediately ordered a new church to be built on the same site, and it was begun the next month.2 Procopius names Anthemius as the man who organized the tasks of the workmen and made models of the future construction, adding: “With him was associated another architect, Isidorus by name, a Milesian by birth, an intelligent man and in other ways also worthy to execute Justinian’s designs.3 Paul the Silentiary concurs in his labored hexameters:“Anthemius, a man of great ingenuity and with him Isidorus of the all-wise mind—for these two, serving the wills of lords intent on beauty, built the mighty church.”4 It is commonly held that Anthemius died in or about 534,5 when Isidorus was left in sole charge, but this must be regarded as unproved. The church was dedicated on 27 December 537.6

In the astonishing space of five years Anthemius and Isidorus erected one of the largest, most ingenious, and most beautiful buildings of all time. The ground plan is a rectangle measuring seventy-seven by seventy-one meters, but the interior presents the appearance of a basilica terminating in an apse, flanked by aisles and galleries, and surmounted by a dome greater than any ecclesiastical dome ever built. The dome rests upon four great arches springing from four huge piers; the pendentives between the arches were at that time a novel device. As in the church of SS. Sergius and Bacchus in the same city, the stresses of the central dome are shared by half domes to the west and east, and the general similarity of plan has led to conjectures that the same architects built the earlier church. The dome nevertheless exerted a greater outward thrust on the piers supporting it than was safe, and when it had to be reconstructed after an earthquake twenty years later it was made six meters higher; but in general the applied mathematics of the architects (no doubt applied instinctively rather than consciously) have proved equal to the exacting demands of fourteen centuries. The decoration of the building was worthy of its artifice; the empire was ransacked to adorn it with gold, silver, mosaics, fine marbles, and rich hangings. Its ambo excited particular admiration.

Anthemius and Isidorus were consulted by Justinian when the fortifications at Daras in Mesopotamia were damaged by floods; but on this occasion the advice of Chryses, the engineer in charge, was preferred.7

Isidorus probably died before 558, for when a section of the dome and other parts of Hagia Sophia were destroyed by an earthquake at the end of the previous year, it was his nephew, called Isidorus the Younger, who carried out the restoration.8 No doubt he had learned his art in his uncle’s office. Essentially what is extant is the church of Anthemius and Isidorus, as repaired by the latter’s nephew and patched after no fewer than thirty subsequent earthquakes, in addition to the ordinary ravages of time.

Isidorus was a mathematician of some repute as well as an architect. Notes at the end of Eutocius’s commentaries on Books I and II of Archimedes’s On the Sphere and the Cyclinder and Measurement of the Circle indicate that Isidorus edited these commentaries.9 The first such note reads, “The commentary of Eutocius of Ascalon on the first of the books of Archimedes on the Sphere and the Cylinder, the edition revised by Isidore of Miletus, the engineer (μéχαντκóζ), our teacher”; and, mutatis mutandis, the other two are identical. It was formerly supposed on the strength of these notes that Eutocius was a pupil of Isidorus; but other considerations make this impossible, and it is now agreed that the three notes must be interpolations by a pupil of Isidorus.10 A similar note added to Eutocius’second solution to the problem of finding two mean proportionals—“The parabola is traced by the diabetes invented by Isidorus of Miletus, the engineer, our teacher, having been described by him in his commentary on Hero’s book on Vaultings”—must also be regarded as an interpolation by a pupil of Isidorus.11 The nature of the instrument invented by Isidorus can only be guessed—the Greek word normally means “compass”—andnothing is otherwise known about Hero’s book or Isidorus commentary on it.

The third section of the so-called Book XV of Euclid’s Elements shows how to determine the angle of inclination (dihedral angle) between the faces meeting in any edge of any one of the five regular solids. The procedure begins with construction of an isosceles triangle with vertical angle equal to the angle of inclination. Rules are given for drawing these isosceles triangles, and the rules are attributed to “Isidorus our great teacher.”12 It may therefore be presumed that at least the third section of the book was written by one of his pupils.

The above passages are evidence that Isidorus had a school, and it would appear to have been in this school that Archimedes’ On the Sphere and the Cyclinder and Measurement of the Circle mdash;in which Eutocius had revived interest through his commentaries—were translated from their original Doric into the vernacular, with a number of changes designed to make them more easily understood by beginners. It is evident from a comparison of Eutocius’ quotations with the text of extant manuscripts that the text of these treatises which Eutocius had before him differed in many respect from that which we have today, and the changes in the manuscripts must therefore have been made later than Eutocius.13


1. “Chronicon Paschale,” in Corpus Scriptorum historiae Byzantinae, X (Bonn, 1832), 621.20-622.2.

2. Zonaras, Epitome historiarum, XIV.6, in the edition by Dindorf, III (Leipzig, 1870), 273.23-29.

3. Procopius, De aedificiis, I.1.24, in his Opera omnia, Haury, ed., IV (Leipzig, 1954), 9.9-16. In another passage Procopius says that “Justinian and the architect Anthemius along with Isidorus employed many devices to build so lofty a church with security”(ibid., I.1.50; Opera omnia, IV, 13.12-15) and in yet another reference he relates how Anthemius and Isidorus, alarmed at possible collapse, referred to the emperor, who in one instance ordered an arch to be completed and in another ordered the upper parts of certain arches to be taken down until the moisture had dried out—in both cases with happy results (ibid., I.1.66-77;Opera omnia, IV, 15.17-17.7). The word translated “architect” in these passages (μéχανoπoτoζ) might equally be rendered “engineer.” There was no sharp distinction in those days. Perhaps “mater builder” would be the best translation.

4. Paul the Silentiary, Description of the Church of the Holy Wisdom, II. 552-555, Bekker, ed., Corpus scriptorum historiae Byzantinae, XL (Bonn, 1837), 28. Agathias, Historiae, V.9, R. Keydell, ed. (Berlin, 1967), 174.17-18, mentions Anthemius alone, but this is not significant; in his account of the church, Evagrius Scholastius—Ecclesiastical History, Bidez and Parmentier, eds.(London, 1898), 180.6-181.14- mentions neither.

5. F. Hultsch, “Anthemius 4,” in Pauly-Wissowa, I (Stuttgart, 1894), col. 2368, “um 534”; followed more precisely by G. L. Huxley, Anthemius of Tralles (Cambridge, Mass., 1959), “in A.D. 534.” But Agathias, V.9, on which Hultsch relies, cannot be made to furnish this date; and the latest editor, R. Keydell, in his Index nominum, merely deduces from the passage pridem ante annum 558 mortuus.

6. Marcellinus Comes, “Chronicon,” in J. P. Migne, ed., Patrologia latina, LI (Paris, 1846), col. 943D.

7. Procopius, op. cit., II.3.1-15; Opera omnia, IV, 53.20-55.17.

8. Agathias, op. cit., 296. Procopius records that the younger Isidorue had previously been employed by Justinian, along with John of Byzantium, in rebuilding the city of Zenobia in Mesopotamia (op. cit., II.8.25; Opera omnia, IV, 72.12-18).

9. Archimedis opera omnia, J. L. Heiberg ed., 2nd ed., III (Leipzig, 1915), 48.28-31, 224.7--0, 260.10-12. The Greek will bear the interpretation that it was the treatises of Archimedes, rather than he commentaries by Eutorcius, which Isidorus revised. This was the first opinion of Heiberg—Jahrbuch für classische philologie, supp. 11 (1880), 359—but he was converted by Tannery to the view given in the text: Archimedis opera omnia, III, xciii.

10. Paul Tannery, “Eutocius et ses contemporains,” in Bulletin des science mathematiques, 2nd ser., 8 (1884), 315-329, repr. in Mémoires scientifiques, II (Toulouse-paris, 1912), 118-136.

11. Archimedis opera omnia, III, 84.8-11.

12. Euclidis opera omnia, J. L. Heiberg and Menge, eds., v (leipzig, 1888), 50.21-22.See also T. L. Heath, The Thirteen Books of Euclid’s Elements, 2nd ed., III (Cambrige, 1926), 519-520.

13. J. L. Heiberg, “Philologische Studien zu griechischen Mathematikern II. Ueber die Restitution der zwei Bücher des Archimedis πέ μέρέτ δέ τητ Ãπατραζ κατ κυλτνδρον,” in Neues Jahrbuch für Philogie und Pädagogik, supp. 11 (1880), 384-385; Quaestions Archimedeae (Copenhagen, 1879), pp. 69-77; Archimedis opera omnia, III, xciii. The delight with which Eutocius found an old book which preserved in part Archimedes’ beloved Doric dialect—έν μέρέτ δέ την‘Aρχτέ πτλν δωπδα γδωÃÃÃν απέÃωχν—shows that there had been a partial loss of Doric forms even before his time.


I. Original Works. Isidors edited the commentaries of Eutocius on Archimedes’ On the Sphere and the Cylinder and Measurement of the Circle. These Survive—with subsequent editorial changes—and are in Archimedis opera omnia, J. L. Heiberg, ed., 2nd ed., III (Leipzig, 1915). A ccommentary which Isidorus wrote on an otherwise unknown book by Hero, On Vaultings, has not survived.

II. Secondary Literature. The chief ancient authorities for the architectural work of Isidorus are Procopius, De aedificiis in Opera omnia, Haury. ed., IV (Leiozig, 1954); Paul the Silentiary, Description of the Church of the Holy Wisdom, Bekker, ed Corpus scriptorum historiae Byzantinae, XL (Bonn, 1837);and Agathias Scholasticus, Historiae, R. Keydell, ed (Berlin, 1967). One of the best modern books is W. R. Lethaby and Harold Swainson, The Church of Sancta Sophia Constantinople (London, 1894). A more recent monograph is E. H. Swift, Hagia Sophia (New York, 1940). There are good shorter accounts in Cecil Stewart, Simpson’s History of Architectural Development, II (London, 1954), 66-72;and Michael Maclagan, The City of Constantinople (London, 1968), pp. 52-62.

For Isidorus’ contribution to the study of the five regular solids, see T. L. Health, The Thirteen Books of Euclid’s Elements, 2nd ed. (Cambridge, 1926; reper. New York, 1956), III, 519-520.

Ivor Bulmer-Thomas

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"Isidorus of Miletus." Complete Dictionary of Scientific Biography. . 23 Aug. 2017 <>.

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Isidorus of Miletus

Isidorus of Miletus (fl. C6). Greek architect, engineer, geometer, and universal man, he worked with Anthemios of Tralles on the design and construction of the great Byzantine Church of Hagia Sophia (Holy Wisdom), Constantinople (532–7). They may also have worked on the Church of the Holy Apostles, Constantinople (c.536–550—destroyed), the model for the Church of San Marco, Venice (begun 1063). When the dome of Hagia Sophia collapsed in 558, it was rebuilt to a modified design by Isidorus the Younger, also from Miletus, probably the elder man's nephew.


Krautheimer (1986);
Mango (1972, 1986);
D. Watkin (1986)

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"Isidorus of Miletus." A Dictionary of Architecture and Landscape Architecture. . 23 Aug. 2017 <>.

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"Isidorus of Miletus." A Dictionary of Architecture and Landscape Architecture. . Retrieved August 23, 2017 from

Isidorus of Miletus

Isidorus of Miletus (ĬzĬdôr´əs, mīlē´təs), name of two architects of the time of Justinian. The elder was associated with Anthemius of Tralles in rebuilding Hagia Sophia, AD 532–37; the younger rebuilt the church's dome after its destruction by earthquake, AD 553.

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"Isidorus of Miletus." The Columbia Encyclopedia, 6th ed.. . 23 Aug. 2017 <>.

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