CONSTRUCTION OF WALLS.
1. Stone wall, constructed according to the principles of the best periods. This wall was constructed with stones of the same size perfectly squared, and in alternate layers, placed either longitudinally or transversely; examples of this perfect kind of construction are found on the quay, near the mouth of the Cloaca Maxima at Rome, an ancient wall of Palestrina, and the remains of a tomb near Albano.
2. Opus incertum, formed of small stones of irregular figures, placed one over the other without order; the angles and extremities of the walls were consolidated by chains of bricks, ranged in horizontal courses, forming a bond at regular intervals; the whole was often covered with a mortar of lime and pouzzolana: the most ancient edifices of Rome appear to have been constructed in this menner, as the cella of the Temple of Tivoli, the remains of the country house of Maecenas and Quintilius Varus; and the Temple of Fortune at Palestrina.
3. Opus reticulatum, reticulated work; this kind of construction, also antique, consisted of small stones of peperino, or tufo, volcanic productions from the environs of Rome; they were cut into small pyramids, about three inches at the base, and five or six inches in height; they were arranged diagonally on the surface of the wall, and the points entered the general mass of rubble of which the wall was composed; there was scarcely any mortar between the joints of the reticulatum, but the whole was gencrally covered with cement. A fine example of the reticulatum is seen in part of the walls of Rome, between the Porta del Populo, and the Villa Borghese, called the Mura torto.
4. Same kind of masonry, in which there was more mortar between the lozenges, but the outer covering of cement was dispensed with.
5. Another kind of reticulatum, a gross imitation of the preceding, but with stones of unequal and irregular form, with a greater quantity of mortar between the joints.
6. Portion of the walls of Rome, restored by order of Narses, in the sixth century; the stones are rudely shaped and separated by large interstices, filled in with brick, and a large quantity of mortar.
7. Another example of the irregular employment of blocks of stone in the construction of the bridge Salaro, rebuilt by Narses in the sixth century.
8. A kind of opus incertum degenerated, seen in a portion of the walls of Rome, restored in the sixth century, by Belisarius; the form of the stones is very irregular, and the joints large with abundance of mortar.
9. Example of a brick wall constructed after the most approved method of the ancients; the two faces of the wall were formed with triangular bricks, with the one angle towards the interior of the wall; the centre was filled in with small stones and mortar; every four feet in heiglit a bond was formed by three rows of square bricks over the whole thickness of the wall; the angles of the walls were similarly strengthened.
10-11. Same kind of construction, but less regular in the arrangement of the bricks and thickness of the joints.
12. Masonry composed of blocks of tufo, arranged in courses, but irregularly, from a wall and tower of a gate of Rome, called de' Cavallegieri, behind the Church of St. Peter.
13. Another wall with blocks of tufo, but employed with more art than the preceding, seen at Rome below the buildings of the capitol; it is a restoration of the fifteenth century; the antique capital and fragment of architrave built in the wall are said to have belonged to the Tabularium, a building destined to preserve the archives.
14. Rude kind of opus incertum, from the ancient tower de' Conti at Rome, executed in the twelfth century, composed of fragments of lava and pebbles, thrown in pell-mell with the mortar, and at unequal intervals in height, are layers of mortar to consolidate the work.
15. Mixed masonry of the third century, from the circus of Caracalla Maxentius near Rome; the surface of the walls formed with alternate courses of triangular and squared blocks of tufo, or peperino; the center of the wall was filled in with rubble.
16. Upper part of the arch of Janus at Rome, in which the same kind of masonry exists, but less regularly executed.
17. Similar construction, from a wall of the Church of S. Angelo in Pescheria, Rome; restoration of the sixth century.
18. Wall built in regular courses, but with blocks of tufo, of unequal sizes, from a building of the thirteenth century, at S. Sisto Vecchio, near the baths of Caracalla.
19. Wall of Lombardic construction, from the ruins of a church at Bergamo, built in courses of three rows of squared stones, and the rows of smaller stones placed angularly.
20. Portion of a wall near the Arch of Titus, composed of fragments of every kind.
21. Construction of the wall of the Church of St. Vincent and St. Anastasius, near Rome, executed from the eighth to the ninth century, by order of Charlemagne, exhibiting an amelioration on the preceding.
22. From the Church of St. Bartholomew at Rome, work of the tenth century, showing that the amelioration did not long continue.
23. The same negligence is seen in a wall of the Church of the Four Saints; eleventh century.
24. The exterior stylobate of the Church of St. Peter, by Michael Angelo, constructed after the principles of the ancients.
25. Façade of a house on which is read "Vinea Vidascha," near the gate of St. Sebastian at Rome; it presents a confused assemblage of antique fragments of Statues and bas-reliefs.
26. Portion of the walls of Rome, restored in 1157, composed of alternate courses of squared stone and long bricks, the whole united with a considerable quantity of mortar.
27. Brick wall from the Church of St. Laurence outside the walls of Rome; thirteenth century.
28. The same construction from a wall of the Church of S. Egidio in Borgo at Rome; fourteenth century.
29. Mixture of tufo and peperino; restored in the fifteenth century by Nicholas V.
30. Walls of the Palace of the Vatican in the sixteenth century, by Leo X; this wall is executed with great care, and may be compared with those of the best periods of antiquity.
31. The same amelioration may be observed in the construction of a bastion erected at Rome near the gate of St. Paul, under Paul III, in the sixteenth century.
CONSTRUCTION OF ARCHES AND LINTELS.
32. Plan and elevation of an archway called the Arco de' Pantini at Rome; the wall is constructed of peperino and the arch stones of travertine.
33. Portion of the Forum of Nerva, called the Colonacce.
34. Part of a façade of an antique edifice at Rome, called the Baths of Paulus Emilius; with the exception of the capitals and the upper cornice, which are in travertine, the whole of the decoration is in brick.
35. Antique gate in Sicily; the jambs of the gate are in squared stone, the arch is formed of three rows of vases of term cotta placed one within the other.
36. Plan and elevation of one of the vases.
37. One of the arches from the Mausoleum of Theodoric, Ravenna.
38. Portion of the cloister of the Church of Sta. Clara, Naples; fourteenth century.
39. From the Palace of the Emperors, Rome.
40. Lintel of brick near the ancient Palace Savelli at Rome.
41. Restoration of the Porta Latina.
42. From St. Nicolas in Carcere, Rome.
43. Flying buttress from the Cathedral of Notre Dame, Paris.
44. Arches of the Farnese Palace at Rome by Vignola; return towards the principles of the ancients.
45. Portion of the antique theater called Castrense.
46. From the wall of a private house, Via di Borgo, Rome.
CONSTRUCTION OF VAULTING.
47. Transverse section of an ancient tomb on the Appian Way, between Rome and Albano.
48. Vault from the Baths of Diocletian at Rome; it consists of chains of brick following the crown of the arch, the intervals filled in with rubble.
49. Hemispheric vault of similar construction, with vases of terra cotta introduced in the spandrils to lighten it.
50. Vault under the steps of the Circus of Caracalla Maxentius near Rome, showing a similar construction.
51. Another example of the employment of vases to lighten the construction of vaulting, from the Church of St. Sebastian, Rome.
52. Covering in stone of the mausoleum of Theodoric at Ravenna.
53. Part of the vault from the House of Pilate, Rome; it is executed in rubble stone, forming a sort of opus incertum.
54. Cupola of St. Vitali, Ravenna, remarkable for its peculiar construction.
55. Transverse section of the vaulting of the nave of the Cathedral of Paris.
56. Vaulting by Michael Angelo under the porticos of the ground floor of the palace of the Conservators at the Capitol.
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