LONDON MINT COIN COMPOSITION, MINT MARKS & STYLE
Last updated: 25 November 2016
Only aes coins -- usually called folles (singular=follis) in modern numismatic texts -- composed of an alloy of copper (by far the largest constituent), tin, lead, silver (and with a silver surface wash) were produced by the London Mint. The size and weight of these coins steadily diminished throughout this period. Coins were initially approx. 28 mm in diameter (approx. 11 grams) gradually declining to approx. 20 mm diameter (approx. 3 grams) -- and less -- by the time the mint closed in 325. Similarly, the silver content declined from approx. 4% to approx. 1%.
The primary Mint mark is engraved on the reverse of the coins in the exergue. The earliest coins (c. 297), a small and rare issue, are marked LON. Other early issues (300 - mid 307) do not have Mint marks . The PLN Mint mark was introduced in the summer of 307 and continued until 314 when it was superceded by the M series marks, to be resumed again in 316 and continued in use until 321 (used concurrently with PLON in the last year of usage). The M series marks: MLL, MSL and MLN were used 314-316. The PLON mark was introduced in 320 and was used until the London Mint closure in 325. Commencing in mid 310, the primary exergue Mint marks are frequently accompanied by a variety of letters/symbols in the reverse field. All of these Mint marks are depicted on coin images throughout these Roman Coins of the London Mint pages.
Coins with LON exergual Mint marks and succeeding unmarked coins
After the restoration of Britain to the Empire Constantius re-opened the London Mint -- now as an official facility with one officina (workshop). After the death of Constantius, this mint continued to operate under Constantine until its closure in 325. The initial issue folles c. 297, again issued in the names of Diocletian & Maximian Herculius as Augustus and Constantius & Galerius Maximian as Caesar, closely followed the design, size and weight of the "Unknown Continental Mint" coinage except they now bore a LON mint mark in the reverse exergue.
Obverse busts face right in this series. The Genius of the Roman People reverse with the legend GENIO POPVLI ROMANI is standard. Genius is depicted standing, head surmounted by modius , naked except for chlamys over left shoulder, holding patera in right hand and cradling cornucopia in left arm. Peripheral legends read clockwise on London Mint coins.
It is now generally accepted that these LON mint marked, and succeeding unmarked, folles were indeed produced in Britain by the London Mint.
References and Resources