Sudbrook, Monmouthshire the Silures from the 2nd century BC and occupied by the Romans from the 1st century AD until the 4th century. The hillfort was originally much bigger than now having been eroded over the centuries. Finds of Roman coins at Black Rock, Portskewett, show that the ferry crossing was in use in Roman times, on the route between the Roman stations of "Aquae Sulis" (Bath) and "Venta Silurum" (Caerwent). According to tradition, Caradog Freichfras, the Welsh ruler of Gwent in the 5th century or 6th century AD, moved his court from Caerwent to the Portskewett area, possibly to the fort.
Aphanizomenon flos-aquae samples exceeded the safety value of 1 µg microcystin per gram. University professor Daniel Dietrich warned parents not to let children consume "A. flos-aquae" products, since children are even more vulnerable to toxic effects, due to lower body weight, and the continuous intake might lead to accumulation of toxins. Dietrich also warned against quackery schemes selling these cyanobacteria as medicine against illnesses such as attention deficit hyperactivity disorder, causing people to omit their regular drugs. A Canadian study studying the effect of "A. flos-aquae" on the immune and endocrine systems, as well as on general blood physiology, found that eating