The unusual cross-shaped Ringerikestil runestone in Skålhamra

The stone's material is gray granite, and the ristning's ornament is in Ringerikestyle, which dates the stone to the period 1010-1050. In the center of the ristning, there is an unusual, cross-shaped cross of a Ryskbysantinsk type, known as a Dagmarskors. This cross is what gives the stone its unique appearance. Above the unusual cross-shaped cross (Dagmarskors), there is a larger Christian cross. To the left of the stone's top, two small, normal crosses can be seen.

It's suspected that there may have been a third cross on the currently damaged upper part. Other types of cross-shaped crosses can be found on various runestones, for example, U 867, U 921, U 1047, U 1074, U 1076, U 1081, and U 1105. The person named in the inscription, 'Ulv in Skålhamra', was the headman of the Skålhamra-släkt. Ulvkell, the person who commissioned the carving, was related to Ulv. Two more runestones can be found near Vallentunasjö, dedicated to the viking and landlord Ulv in Skålhamra, namely U 225 and U 226. Ulv in Bårresta is also mentioned on U 336.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons