Collecting campgates is one of the more popular themes for Roman coin collectors. These coins cover more than one hundred and fifty years; with most of the rulers represented. There is a debate about what is actually portrayed on the reverse. Are they military campgates or city gates. The most prolific reverse type is the PROVIDENTIAE AVGG; which translates as " [In honor of] The Foresight of the Emperors." This might just merely be a slogan praising all the Emperors for the security of the Empire; so more of an abstract thought, rather than a specific type of construction. These campgates should not be confused with coins from Roman provinces; which certainly issued coins with city gates. However, the argument for campgate is strengthened by the reverse type issued by Valentinian III. This reverse was CAST VIC and castrum is a Roman camp/fort.
Here are some of my favorites.
Campgates started in silver and there are a few reverses with VIRTVS MILITVM being the most common.

Diocletian
A.D. 294
AR Argenteus 18mm 3.3g
DIOCLETIANVS AVG; laureate head right.
VIRTVS MILITVM; four tetrarchs sacrificing over tripod before gate in six turreted enclosure.
RIC VI Rome 27a

Maximinus II
A.D. 308
AE follis 26mm 6.1g
GAL VAL MAXIMINVS NOB CAES; laureate head right.
VIRTVS MILITVM; campgate with portcullis surmounted by four turrets.
In ex. MKΓ
RIC VI Cyzicus 40

Constantine I
A.D. 325
19x21mm 3.3g
CONSTAN-TINVS AG; Laureate head right.
PROVIDEN-TIAE AVGG; campgate with two turrets and star between them, dot in bottom of doorway.
in ex. PLON dot
RIC VII London 294 variation; LMCC 10.02.002 (this coin cited and illustrated)
here's a fancy martial bust from Rome

Constantine I
A.D. 318- 319
19mm 3.1g
CON-STANTI-NVS AVG; cuirassed and helmeted bust left, spear pointing forward and shield on left arm.
VIRTVS AVGG; campgate with closed doors and three turrets, across fields P-R
In ex. RP
RIC VII Rome 178
18 rows...the most I have seen on a campgate

Constantine I
A.D. 328-9
18x19mm 3.1g
CONSTAN-TINVS AVG; Laureate head right
PROVIDEN-TIAE AVGG; campgate with 18 rows, two turrets, no doors, star above.
in ex. delta SIS double crescent
RIC VII Siscia 214
if you want a campgate from Sirmium, it has to be Constantius II

Constantius II
A.D. 324- 325
AE nummus 18mm 3.3g
FL IVL CONSTANTIVS NOB C; Laureate, draped and cuirassed bust left.
PROVIDENTIAE CAESS; campgate with two turrets and star between them.
in ex. SIRM
RIC VII Sirmium 53
Crispus campgates from Constantinople are scarce, due to his being executed around this time

Crispus
A.D. 326
19mm 2.7g
CRISPVS NOB CAES; Laureate, draped and cuirassed bust right.
PROVIDEN-TIAE CAESS; campgate with two turrets and star between them; in left field B.
in ex. CONS
RIC VII Constantinople 8

Valens
A.D. 364- 378
AE nummus 22mm 4.4g
D N VALEN-S P F AVG; pearl-diademed, draped and cuirassed bust right.
GLORI-A ROMA-NORVM; campgate with two turrets, no doors; S above.
in ex. SMTR
RIC IX Trier 29b

Theodosius I
A.D. 384- 388
20mm 2.3g
D N THEODO-SIVS PF AVG; pearl diademed, draped in imperial mantle, holding mappa and scepter.
GLORIA REI-PVBLICE; campgate with two turrets, Tau-Rho between them.
In ex. TES
RIC IX Thessalonica 59b

Valentinian III
A.D. 425-455
11mm 1.2g
[D N VALEN AVG]; pearl-diademed, draped and cuirassed bust right.
[CAST] VIC; campgate with no doors and two turrets, star above.
RIC X Rome 2163
if you enjoy campgates, my page with over 100 is here--
https://constantinethegreatcoins.com/campgates/