The tombstone of Vivius Marcianus was found during the rebuilding of St Martin’s Church on Ludgate Hill in 1669 (RIB 17). (The church itself had been destroyed in the Great Fire of London in 1666.) The gravestone was then placed in the Ashmolean Museum (that opened in 1683); it is now displayed in the Museum of London (since 1974). It is likely that this came from the cemetery outside (and to the west) of Ludgate.
Vivius Marcianus is described as a centurion of the II Augustan Legion. He is shown in the relief holding the centurion’s stick, vitis, in his right hand. The legion was based at Caerleon in south Wales. There is a possibility that he was attached to the staff of the governor.
The monument was set up by Januaria Martina, his wife.
Heritage Futures 
For 1852 drawing of the inscription
https://www.britishmuseum.org/collection/object/P_1874-0314-234