XX, 20 sesterces - on the first gold coins struck for the Roman republic at Capua in 217 BC. Other marks of value found on these coins are [anchor, flukes down]X 60 sesterces and XXXX 40 sesterces.
XX, as a mark of value on the copper coins of the Ostrogoths without name of king.
XX Vicennales (?) - PRIMI XX IOVI AVGVSTI (sic IOVII) - on a rare gold coin of Diocletian.
XX (Vicennalia ?) - DIOLETIANI AVG or MAXIMIANI AVG, within a laureal wreath, on gold coins of Diocletian and Maximian Hercules.
XX Vicennalibus - VOT XV FEL XX OR VOT XV MVLT XX, VOT XX SIC OR MVLT XXX, etc. See X Decennalibus
XX Viscesima, Vicesimo, Vicesimum, and similarily with the compounds of XX up to XXIX or XXVIIII. See X Decimum
XX, within a laurel wreath; in the exergue, AQ (Aquiliae) or CONST (Constantinae - Arles), or LVG (Lugduno). Obverse CAESAR, head of Constantius Gallus to right, bare head. Silver medallion. Froehner suggests that the XX on these medallions indicates the value of the peces of which the weight equalled 1/24th of the silver pound.
XX - PXXT, SXXT, TXXT, QXXT, VXXT, VIXXT. Prima, Secunda, Tertia, Quarta, quinta, Sexta, XX Tarracone - on coins of Aurelian and Probus. "On the accession of Aurelian (AD 270-275) to the throne heattempted to remedy the disordered state of the coinage, and to restore it from its degraded state under Gallienus. His first object was to put to an end to the continual fluctuations in the price of gold, caused by the quantity of base money which was issued from the imperial mint. To effect this with as little injury as possible, he reduced the base denarii in circulation to the rate at which they then circulated, which appears to have been 500 or 525 to an aureus, and consequently issued from the mint pieces equal to 20 or 21 of these copper denarii as equivalent to a denarius of account. The weight of the common copper and pated coins of Aurelian and his successors, which have XX and XXI in the exergue, varies from 56 to 66 grains [3.63 to 4.28 grams], and consequently from 20 to 21 are equal to four of the large copper coins, or sesterces, of Severus Alexander and Gordian III." The numbers XX and XXI occur also on the coins of Probus, but the former was discontinued after his reign, whilst the latter occurs to the time of Constantine the Great. See VXXT, VXX, and Tarraco, Karthago.