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* the barracks of the praetorian guard, built by Tiberius at the instigation of Sejanus in 21-23 A.D. when these troops were quartered permanently within the city (Suet. Tib. 37; Tac. Ann. iv. 2; Cass. Dio lvii. 9. 6; Schol. Iuv. x. 95). They were in the extreme north- eastern part of Rome, just beyond the inhabited district (Plin. NH iii. 67 ; Suet. Nero 48; Not. Reg. VI), about 500 metres east of the agger, on a site that was one of the highest in Rome (59-60 metres above sea-level), and commanded both the city and the roads leading to the east and north-east. The camp was constructed on the usual Roman model, forming a rectangle 440 metres long and 380 wide, with rounded corners. The longer axis, the cardo maximus, ran nearly north and south, and at its ends, in the middle of the shorter sides, were the porta praetoria and the porta decumana. It is not certain, however, whether the porta praetoria was on the north side or the south (HJ 387-388 north, Antonielli, BC 1913, 31-47 south). The cardo maximus did not divide the castra equally, and the gates at its ends, porta principalis dextra on the west and porta principalis sinistra on the east, were 190 metres from the north side and 250 from the south.1

The original walls of Tiberius (AJA 1912, 398) are of brick-faced concrete, 4.73 metres high where they are still preserved (see below), and had battlements and turreted gates (Ill. 13) (Tac. Hist. iii. 84; Herod. vii. 11.12). On the inside of the wall were rows of vaulted chambers occupied by soldiers, some of which, on the north and east sides, are still visible. They were 3 metres high, of opus reticulatum lined with stucco, and above them ran a paved walk for the guards (for the discovery of these and other chambers in the castra, see BC 1872-3, 5, 12-14; 1876, 176-178). A view of the principia is perhaps to be found on one of the 'Aurelian' panels of the Arch of Constantine (PBS iii. 263). As would be expected from the importance of the praetorian guard, the castra are mentioned frequently in the literature of the empire (Tac. Ann. xi. 31; xii. 69; xiii. 14; xv. 53, 59; Hist. iii. 84; Suet. Claud. 21; Hist. Aug. Did. Iul. ii. 6; Balb.x. 5; Frag.Vat. 195; Herod.ii.6,7; vii. II, 12; Chron. 147) and in inscriptions (CIL vi. 9277, 9661, 9992), especially those on lead pipes, which show the care expended by successive emperors on the water supply of the barracks (CIL xv. 7237-7244;2 LA 438-442, Nos. 103-127).

Two interesting coin types of Claudius represent on the reverses his reception in the praetorian camp after the murder of Caligula: the legends are respectively imper(ator) recept(us), which is shown in the type with a soldier on guard, and praetor(ianus) recept(us) (i.e. infidem), i.e. the acceptance by Claudius of the fealty of the praetorians-an idea well symbolised by the clasping of hands (BM Imp. p. cliii; Claud. 5, 8-10, 20-25, 28-37, 38 and p. 174 n.. =Cohen, Claud. 40- 46, 77-80).

The regular name of the barracks was castra praetoria, but they seem also to have been called vulgarly castrum praetorium (CIL xv. 7239 b, c) and castrae praetoriae (ib. d); and in the Middle Ages castra custodiae (BC 1914, 399, 402). The cohortes urbanae were also quartered here before the construction of the Castra Urbana.

Aurelian incorporated the castra in his line of fortification, which joined the castra at the north-west corner and again near the middle of the south side. The north and east wall of the castra thus formed the continuation of the Aurelian wall, and its original height was increased by an addition of 2.5 to 3 metres at the top and by digging away the soil about its foundations to a depth of 2.3 metres (Homo, Aurelien 244-245, 266-268). The original wall can be distinguished from that of Aurelian by the difference in brickwork and by the outline of the battlements (LR fig. 171 shows Aurelian's battlements, and not those of Tiberius; for the latter, see RA 41-46, and especially fig. 46, in which both the lines of battlements are seen). The gates on the north and east sides were also walled up by Maxentius (?). In 312 Constantine disbanded the praetorian guard and dismantled their barracks, presumably by destroying the inner walls that had not been used by Aurelian (Zos. ii. 17; Aur. Vict. Caes. xl. 25; Lact. de mort. pers. 26), although a part of the west wall is reported as standing in the sixteenth century (LS ii. 243; HJ 389, n. 41).

Within the castra was the shrine of the standards of the guard (CIL vi. 1609; Herod. iv. 4. 5; v. 8. 5-7), a tribunal, on which these standards were set up, restored by the statores attached to the barracks (CIL vi. 3559; WS 1902, 356-358), a shrine of Mars (CIL vi. 2256), and an armamentarium, or imperial armoury, mentioned twice by Tacitus (Hist. i. 38. 80) and in two inscriptions (CIL vi. 999, 2725; RE ii. 1176).

In the north part of the castra, east of the north gate, was an altar of Fortuna Restitutrix, of which the remains were found in 1888 in a room paved with black and white mosaic (NS 1888, 391 ; BC 1888, 401; CIL vi. 30876).3 Certain antiquarians of the sixteenth and fifteenth centuries speak of an arcus Gordiani near the porta Chiusa (for reff. see HJ 390, n. 45; LS i. 169; BC 1913, 38), and this has been connected by some with architectural fragments found in the via Gaeta and the viale Castro Pretorio (BC 1872-3, 103, 233-237). One or more such arches may very probably have stood in or near the castra, but there is no evidence of an arch of Gordian, or that the fragments discovered belonged to that arch mentioned in the Renaissance (BC 1913, 37-42). For further discussion of the castra, see Gilb. iii. 198-199; HJ 385- 390; LR 439-442 (the relief from an arch with a Victory is at Ny-Karlsberg, No. 511); for tabulae lusoriae found within it, BC 1877, 81-100; for inscribed amphorae in the camp and vicinity, BC 1879, 36-112, 143- 195; 1880, 82-117; CIL xv. 4529-4898 passim). The latest study of it is in PBSx. 12-22 (by I. A. Richmond).

1 This has been the view hitherto; but Richmond points out that the arrangement of the barracks shows that the via principalis (which on the analogy of all other camps must have run through in a straight line) can only have run from north to south, the east to west line being interrupted. He therefore places the porta praetoria on the west, the decumana on the east, and the porta principalis dextra and sinistra on the north and south respectively (PBS x. 13).

2 The provenance of ibid. 7245 is uncertain, and it apparently refers to a centurion of the first cohort of the vigiles.

3 This inscription (cf. also RE vii. 35) belongs to the Severan period, and repairs at that time are vouched for by brickstamps (CIL xv. 3: Castris praetori(s) Aug. n.) which should be attributed to this period rather than to that of M. Aurelius and Commodus. The bearded head is found again on CIL xv. 381 (PBS x. 22 n. 4). A Christian cemetery of the beginning of the sixth century was also found in the castra (De Rossi, Roma Sott. i. 218; Grisar, Geschichte Roms, i. 668).

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