Vartiokylä hill fort is one of the most prominent historic sites from the age before Helsinki city was established. The fortification dates from the 13th and 14th centuries and it has been in use only for a short period. It is unknown who built it but probably the hill was fortified by Swedish-speaking settlers, crown or some local noble (like Bo Jonsson Grip).
During the first World War Russians built trenches to Vartiokylä hill as part of the Helsinki fortification system. Today you can still see remains of medieval stone foundations.
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.