Grosnez Castle is a ruined castle built by Sir John des Roches around 1330. The castle's purpose was to provide local farmers with a place of refugee from French attacks. The French captured however the castle in 1373 and 1381. The castle was probably demolished around the time of the French occupation of Jersey (1461–1468). In 1483 the Seigneur of St Ouen was allowed to fortify his manor house and it is unlikely he would have been given permission if Grosnez was still in use. In 1806, a naval signal station was established at Grosnez to send messages to Guernsey.
The castle's position on a clifftop 60 m above the sea means that the natural features of the site protect it on three sides. A ditch dug into the rock provides protection on the fourth side. The remains of ruined walls, mostly footings, are still present. A drawbridge and portcullis protected the gatehouse, which is the only substantial surviving remnant, and would have made it difficult to capture. There are traces of six simple buildings.
The name comes from the old Norse words for 'grey headland' - grar nes - an accurate description of the site when seen from the sea, rather than from the French for big nose. A nearby headland to the west has a similar name, Rouge Nez.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.