Bath city walls the Romans, to surround their town (known then as "Aquae Sulis"), probably in the 3rd century. The Anglo-Saxons by the 10th century had established Bath as a fortified "burh" (borough), utilising the existing town walls, and maintaining Bath as a centre of regional power. Bath, located on the northern edge of the kingdom of Wessex, would have guarded against any attack from neighbouring Mercia, which was held by the Danes for a time. The height of the walls was increased on the orders of King Stephen during The Anarchy. Bath's medieval walls included four gates. The North and South Gates
Aphanizomenon flos-aquae Aphanizomenon flos-aquae Aphanizomenon flos-aquae is a brackish and freshwater species of cyanobacteria found around the world, including the Baltic Sea and the Great Lakes. "Aphanizomenon flos-aquae" can form dense surface aggregations in freshwater (known as "cyanobacterial blooms"). These blooms occur in areas of high nutrient loading, historical or current. "Aphanizomenon flos-aquae" has both toxic and nontoxic forms. Most sources worldwide are toxic, containing both hepatic and neuroendotoxins. Most cyanobacteria (including "Aphanizomenon") produce BMAA, a neurotoxin amino acid implicated in ALS/Parkinsonism. Toxicity of "A. flos-aquae" has been reported in Canada, Germany and China. "Aphanizomenon flos-aquae" is known to produce endotoxins, the