The campgate motif is one that appears in Roman coinage and continues in some form into later Western European coinage. Whether or not the Carolingian gates are reflective of campgates or simply city gates is not clear, and the case can be made either way. The campgate motif became popular in Roman coinage in the 4th century. The campgate pictured above (and described more fully below) is typical of these gates - generally a gate set in a wall/tower surmounted by turrets (or beacons). The surviving gate at Trier allows us to see the commonalties between the reality and the coin. The Trier campgate, surviving today, was essentially the entrance to a fortified area and not a part of a transient camp.

Here is a set of representative (and common) 4th century campgate coins, going from Licinius to Constantius. These are followed by a Carolingian gate coin.

Follis (? -silver wash over copper on rev.), 21mm. Obv: IMP LICI/NIVS AVG, head left. Rev: PROVIDEN/TIAE AVGG, central campgate with three turrets, each on a three legged base, dot over circular turret. Gate wall has 6 rows, gate three rows high. Mint: -HT-, Heraclea. Obv. Van Meter Licinius ol/4, rev. Licinius Jr. #8. Obv and rev don't match to same ruler in VM.

Top left: AE3, 19mm. Obv: CONSTAN/TINVS AVG, head right. Rev: PROVIDEN/TIAE AVGG, center campgate with two turrets. Each turret is three legged. Central eight point star between the turrets. Gate wall has eight rows of blocks, gate is 5.5 rows high. Mint: SMKgamma pellet - Cyzicus. VM obv. ol/12 #85. This coin is paired with the Carolingian coin in the top image.

Top right: AE3, 18mm. Obv:  CONSTAN/TINVS AVG, head right. Rev: PROVIDEN/TIAE AVGG, center campgate with two turrets. Each turret is circular and three legged. Star between turrets. Gate wall has eight rows of blocks, gate is 4.5 rows high. Mint SMKA - Cyzicus. VM obv. ol/12 #85.

Bottom left: AE3, 20mm. Obv:  CONSTAN/TINVS AVG, head right. Rev: PROVIDEN/TIAE AVGG, center campgate with two turrets. Each turret is circular and three legged with a dot on top. Any star between the turrets is obscured on this coin. Gate wall has six rows of blocks, gate is 4 rows high. Pellet in the reverse right field. Mint SMTSA is Thessalonica. VM obv. ol/12 #85.

Bottom right: AE3, 19mm. Obv:  CONSTAN/TINVS AVG, head right. Rev: PROVIDEN/TIAE AVGG, center campgate with two turrets. Turrets are circular and three legged with a dot on top. There is a star between the turrets. Gate wall has six rows of blocks, gate is 4 rows high. The top row of blocks has dots in each of five arches. Mint SMTS epsilon  Thessalonica. VM obv. ol/12 #85.

AE3, 19mm. Obv: CONSTANTINVS IVN NOB C, bust left. Rev: VIRTVS CAESS, center campgate with four turrets. Turrets are more phallic, star (?) between central three legged turrets. Gate has four rows of blocks. Gate has open doors. Mint QAcrescentRL, Arelatum/Constantia. VM obv. ol/4 #42.

Left: AE3, 21mm. Obv: FL IVL CONSTANTIVS NOB C, bust left. Rev: PROVIDENTIAE CAESS, central campgate with two three legged turrets turrets with a dot on top of the circle and central eight point star. The gate has eight rows of blocks with the gate being four rows high. Coinage is prior to 335. Mint is SMHT - Heraclea. Pellet in the reverse left field. VM ol/6 #70.

Right: AE, 19mm, copper. Obv: FL IV CONSTANTIVS NOB C, bust left. Rev: PROVIDENTIAE CAESpellet, central campgate with two three legged turrets and central eight point star. The gate has seven rows of blocks with the gate being 3.5 rows high. Coinage is prior to 335. Mint is NB - Nicomedia(?). VM ol/6 #70.

For a further discussion of Roman campgates, see an interesting campgate piece by Doug Smith. I appreciate identification help from Beast at Beastcoins.com.

AR denier 19mm. 1.69 gr. class 1, 840-65. Obv: +CARLVS REX FR, central cross in a circle, besants in each quadrant. Rev: +AVRELIANIS, central camp gate. Orleans mint. The alignment of the gate places the + at the bottom of the coin and starts the legend in the lower left, as per later coins. Charles' gate is very similar to that of his father and grandfather (Louis the Pious and Charlemagne), but the obverse is similar to another Charlemagne format, not his IMP AVG legend. R1267; MGv 944 (they identify a variation with only a + beneath the gate rather than .+. This weight is heavy compared to their citations.) Dep 9D1, 725 (71 examples); Bel 77; seller (Singer) id Prou 511, MEC 835.

Gate or campgate? The argument can be made either way that the Carolingian gate is a direct reflection of the Roman campgate or that it is just a stylized (city) gate. I think the stronger argument is for similarity to the Roman campgate motif.

First, the argument that it is a deliberate representation of the Roman campgate motif. Charlemagne was crowned emperor in December 800 by Leo III. He was acclaimed to shouts of  "To Charles Augustus, crowned by God, great and pacific emperor of the Romans, life and victory." (Halphen 90, Chamberlin (194) gives a slightly different version.) In the next Spring he took the title "Romanum gubernans Imperium" ("governing the Roman Empire") and later called himself Charles, Most Serene Augustus, etc." (Chamberlin 204). A contemporary pope (Leo III?) referred to him as "novus Constantinus," or the new Constantine. He clearly saw himself as the successor to Roman emperors.

Carolingian military orientation reflected its predecessor's traditions. Bachrach, speaking of Aquitaine, notes (p.5) "The major cities, most of which had been walled and fortified since the late Roman empire were garrisoned." He notes the continuity of military traditions (p.8), "The continuity in military organization in Aquitaine from the Merovingian era to the period of independence (from Merovingian control) is worth emphasizing...special units deployed largely for garrison duties - persist and flourish" And later, (p.9) "Pippin's (le Bref) military objectives therefore were similar in many ways not only to those pursued by the Visigothic kings who seized Aquitaine from Rome and garrisoned its strong places but also to those of the Merovingians who drove out the Goths and later fought over the same region in their civil wars." In other words, there is a direct continuity of fortified and garrisoned communities from the late Roman times to the Carolingians.

Now to the coin link. Charlemagne had limited coinage struck after 812 (plenty of time for the mantel of the Imperium to settle into the Frankish consciousness) that is decidedly Roman in character.

The obverse legend is CARLVS IMP AVG with a very Roman portrait. The reverse is a stylized gate, with the mint in the legend. Given his identity with the Roman Imperium, his titles, and his identity with Constantine the Great,  and the history of garrisoning strong points, it would not be a surprise that a militarily oriented Roman coin style was would be attractive to imitate and find its way into Carolingian coinage. Once picked up by Charlemagne, it was imitated by his son (Louis the Pious) and grandson (Charles the Bald). The gates even appear to be topped by turrets, as is common on Roman coins. These images, and the ones immediately below, are from J.N. Roberts. The mints for these coins are, l to r, Arles, Lyon, Rouen and Trier.

Mayhew (p11-2) describes this coinage as "distinguished by a deliberately Constantinian type profile bust on the obverse. The laurel wreath and military cloak display the new emperor with all the appropriate attributes." He does, however,  go one to say that "some of the greater cities ... marked their status by setting a city gate on the reverse."

As noted this imperial style continues with Louis the Pious.

Louis continues to use the HLVDOVVICVS IMP AVG legend on a very Romanized coin, with a reverse similar to Charlemagne's. The mints are, l to r, Arles, Arles, Orleans, Pavia.

Hence, one can reasonably come to the conclusion that the Carolingian gate is in fact a reference to the Roman campgate of 4th century coinage.

For a different point of view, the (weaker) argument can be made that the Carolingian gate is really a reflection of a city gate unrelated to a military camp. The argument has to rest primarily on design characteristics. By the time of Charlemagne's coinage, the kingdom had secured its interior borders and and the role of garrisoning in the core empire had become reduced in significance (an undocumented assertion made based on internal empire cohesiveness). Charlemgne's (and his successors) gates differ in several ways. It differs in terms of size of gate, with the Carolingian gate generally being smaller than the Roman coin campgate. The Carolingian wall lacks the detail present in the Roman gate wall. Finally, the squareness of the Carolingian gate differs from the arch of the Roman coin campgates.

By the early 9th century, in contrast to the Romans, the Carolingians, did not maintain a standing army. The Franks were certainly warlike and engaged in annual campaigns, but mobilizations generally happened in the Spring and were over by the Fall. Local officials (counts) were responsible for raising the annual levees and each person was responsible for providing his own provisions (Halphen 118-22). After the annual campaign, the troops were commonly dispersed to their homes. Hence, militarily the Carolingians came to be organized differently from the Romans and the idea of the campgate would not be meaningful to them.

On the other hand, the experience of barbarian invasions was recent in their memory and communities would have been fortified. Paris was walled from an early time, as were other communities. Therefore, the gate reflected on the Carolingian coins may actually have been a city gate rather than reflect an essentially military campgate.

An English addendum:

Marvin Tameanko, in response to this page, offered a better researched explanation. He says, in private correspondence "I offered a slightly different conjecture in my book 'Monumental Coins' and in an article on the coins of Charlemagne done for the Classical and Medieval Numismatic Society, CMNS.  My theory is that the 'gate' on Carolingian coins is the local, so called, 'Large Altar', actually a shrine enclosure for an altar built by the Romans for Roma and Augustus. These can be seen on coins of Augustus struck in Lugdunum, RIC, 230. and see page 216-18 of my book.  Compare Augustus' Altar of Lugdunum to the gate of Lugdunum on Carolingian coins.  They are almost identical. These 'Altars' were converted into Christian churches and the Carolingians, whose goals included converting all the pagans in their domains to Christianity, promoted the religion on their coins by featuring these new churches. Note the cross below the structure. The so-called Roman 'camp gate' (I still insist they were CITY gate/triumphal arches) were exhibited to advertise the defenses and security of a city."

After the Carolingian era, the gate motif continued on some coins, particularly those from Orleans. These were minted by Hugues, son of Robert II, Philip I and his successors, Louis VI and VII. Here are Hugues', Philip's and Louis VI's Orleans coins.

The coin: AR denier, 20mm, 1.34g. Obv: +D-I DEXTRA BE, portal with letters HYGO around it. Rev: +AVRELIANIS CIVITAS, central cross. Mint is Orleans. C 31aV (BE, not BNE in the reverse). R4895 as an anonymous issue; not in Dup, PdA. Ciani places as a royal coin in Robert's name.

Denier, 22mm. Obv: +PHILIPVS X REX D-I, central gate. Rev: AVRELIANIS CIVITAS, central cross with 's' in two quadrants. Mint is Orleans. D56/57, not in C.

Denier, 20 mm. Obv: +LVDOVICS REX I, cross with ‘o' in one quadrant and ‘y' in the opposite. Rev: +AVRELIANIS CIVITAS, with an ‘o' under the stylized city gate (mint: Orleans). D120, C111.

An English addendum:

Thanks to Dave Tranbarger for flagging the existence of this English coin, and to Marvin Tameanko for his insights.