There are, however, many remains of Anglo-Saxon church architecture. At least fifty churches are of Anglo-Saxon origin with major Anglo-Saxon architectural features, with many more claiming to be, although in some cases the Anglo-Saxon part is small and much-altered. It is often impossible to reliably distinguish between pre- and post-Conquest 11th century work in buildings where most parts are later additions or alterations. The round-tower church and tower-nave church are distinctive Anglo-Saxon types. All surviving churches, except one timber church, are built of stone or brick, and in some cases show evidence of re-used Roman work.