Roman London declined during the later second century, through the “crisis” of the third, and into the fourth, during which time the Roman Empire as a whole came under increasing attack from within as well as without – Britain was ruled by its own rival Emperors Clodius Albinus in the late second century, and Carausius and Allectus in the “Carausian Revolt” of the third, after which latter, it was retaken by the Emperor Constantius Chlorus in 296. It appears that many of Roman London’s public buildings, including the “Governor’s Palace”, the Basilica and Forum, and possibly also the Amphitheatre, were substantially demolished at the turn of the third and fourth centuries – perhaps as punishment for its perceived support of the “Carausian Revolt”. “Barbarian” raids – by Picts and Scots, and by Saxons and other Germanic tribes – began in the fourth century. The city finally fell, and was essentially abandoned, in the early fifth, around 410, when the legions were recalled to Rome on the orders of the Emperor Honorius.
New building works from this period include:
the City wall, dating to the late second to early third century,
and the river wall, dating to the mid to late third (*);
the Temple of Mithras, dating to the early third century;
and an enigmatic, only partially excavated, building, variously interpreted as a late Roman Basilica or – on the basis of similarity to the Basilica di Santa Tecla in Milan – a “palaeo-Christian” church or cathedral, between Pepys Street and Trinity Square, dating to the fourth century.
(*) There being no local source of stone, the wall was constructed out an estimated 85000 tons of Kentish Ragstone, quarried near Maidstone and transported down the Medway and up the Thames to London on barges, the remains of one of which have been found at Blackfriars, with its 50-ton cargo intact.