The Limfjord (common Danish: Limfjorden , in northwest Jutlandish dialect: Æ Limfjord) is a shallow part of the sea, located in Denmark where it has been regarded as a fjord ever since Viking times. However, it now has inlets both from the North Sea and Kattegat, and hence separates the North Jutlandic Island (Danish: Nørrejyske Ø, which includes the old provinces of Vendsyssel, Han herred and Thy) from the rest of the Jutland Peninsula. The Limfjord extends from Thyborøn Channel on the North Sea to Hals on the Kattegat. It is approximately 180 kilometres (111 miles) long and of an irregular shape with numerous bays, narrowings, and islands, most notably Mors, and the smaller ones Fur, Venø, Jegindø, Egholm and Livø. It is deepest at Hvalpsund (24 metres). Its main port is Aalborg, where a railway bridge (Jernbanebroen over Limfjorden) and road bridge (Limfjordsbroen) have been built across the Limfjord to Nørresundby, while motorway E45 crosses it through a tunnel to the east. Commercial ports also exist at Thisted, Nykøbing Mors, Skive, Løgstør, Struer, Lemvig and Thyborøn. There are also bridges at Oddesund, Sallingsund, Vilsund, Aggersund and Sebbersund, and a number of ferry crossings. History Western opening From the early Middle Ages until 1825, the Limfjord was only open to the sea at its east end. In that year, the North Sea broke through from the west and created a second opening, turning the northern part of Jutland Vendsyssel-Thy into an island. An isthmus of shifting sand has separated the Limfjord from the North Sea during historic times. The present inlet, Thyborøn Channel, has existed only since 1862. A passage also existed during the Viking Age. Based on place names and the geography it is thought to have been to the south of the present one, between Ferring Sø (locally still called 'the Fjord') and Hygum Nor. Canute the Great sailed into it in 1027 on his way back from England. According to Saxo Grammaticus it closed at some time around 1200. There are records of several floods piercing the isthmus during the 16th to early 19th century. On 3 February 1825 a flood pierced a permanent opening, the so-called Agger Channel, in the north of the 13 km long and less than 1 km wide isthmus, the Agger Tange, which had until then linked Thy with the rest of Jutland. The western part of North Jutland lost its road