The prison is built on sandy ground making it relatively easy for prisoners to dig tunnels.The Alcacuz prison, in the northeastern city of Natal, is now the battleground in an escalating war between Sao Paulo-based First Command, Brazil’s largest criminal gang, known by the Portuguese acronym PCC, and local gang Crime Syndicate of Rio Grande do Norte. Officials even put up an improvised wall of metal shipping containers to separate the two inmate faction groups, planning to replace containers with a concrete wall. Alcacuz prison was designed to hold 620 inmates, but held more than 1,000 before the riot erupted. The outbreak of violence after the New Year is the latest in Brazil’s beleaguered penitentiary system. The government of Rio Grande do Norte announced on Monday a series of emergency measures to try to retake control of the State Penitentiary of Alcaçuz, near Natal.