Troo bears a certain resemblance to the city of Og. Originally it was all underground, but in process of time it effervesced, bubbled out of its holes, and is now but half troglodyte. The heights that form the Northern declivity of the valley of the Loir come to an abrupt end here, and have been sawn through by a small stream creating a natural fosse, isolating the hill of Troo that is attached to the plateau only on the North. The hill rises steeply from the river to a crest occupied by a Romanesque church recently scoured to the whiteness of flour, and beside it is a mighty tumulus, planted with trees.