Galileo's championing of heliocentrism was controversial within his lifetime, when most subscribed to either geocentrism or the Tychonic system. He met with opposition from astronomers, who doubted heliocentrism due to the absence of an observed stellar parallax. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was false and contrary to scripture, placing works advocating the Copernican system on the index of banned books and forbidding Galileo from advo defended his views in Dialogue Concerning the Two Chief World Systems, which appeared to attack Pope Urban VIII, thus alienating not only the Pope but also the Jesuits, who had both supported Galileo up until this point.