The Nabataeans were allies of the first Hasmoneans in their struggles against the Seleucid monarchs. They then became rivals of the Judaean dynasty, and a chief element in the disorders that invited Pompey's intervention in Judea. According to historian Paul Johnson, many Nabataeans were forcefully converted to Judaism by Hasmonean king Alexander Jannaeus. It was this king who, after putting down a local rebellion, invaded and occupied the Nabataean towns of Moab and Gilead and imposed a tribute of an unknown amount. Obodas I knew that Alexander would attack, so was able to ambush Alexander's forces near Gaulane destroying the Judean army (90 BC).