If you visit some of Essex’s islands on a simple day trip from Havering, you can walk in the footsteps of Vikings, says Prof Ged Martin

There are about thirty islands around the Essex coast. It’s hard to be precise. Some are low-tide mudbanks. Some, like Bridgemarsh in the Crouch, have effectively been abandoned.

Canvey and Wallasey have bridges to the mainland. So has Two Tree Island, a nature reserve within walking distance of Leigh-on-Sea station.

Causeways to Mersea and Northey in the Blackwater are covered at high tide for several hours. Visitors should check times in advance.

Osea in the Blackwater is privately owned. Public access to the defence installations at Foulness is severely restricted.

Wallasea Island is just thirty miles from Gallows Corner – and most of that is speeding down the A127. Head north from Rochford towards Ashingdon, then follow signs to Burnham Ferry.

The Royal Society for the Protection of Birds is converting much of Wallasea into a wetland bird sanctuary.

Millions of tonnes of spoil from Crossrail excavations have been dumped to create a new landscape.

The RSPB says it’s “early days” in this major project, coded message for “there are no loos”.

But you can still walk the riverside walls, enjoying the marshland vistas and the view across to the quayside at Burnham-on-Crouch, with its fleets of yachts.

The National Trust aims to make Northey Island, in the Blackwater, publicly accessible – whenever tides permit. You’ll need to do your website homework here, not least because visitors are asked to telephone the island’s resident warden to say when they’re coming.

Pay parking is available in Maldon, a mile away. The stroll to the causeway crosses one of England’s oldest battlefields.

In 1991 AD, marauding Vikings occupied Northey.

Local Saxon boss Byrhtnoth mobilised the men of Essex, and fighting broke out to control the causeway.

Eventually the Vikings pointed out that if they were allowed to cross, there could be a proper battle on the mainland.

Byrhtnoth agreed. The result was the slaughter of his army. Byrhtnoth’s head was never found.

That’s the trouble with us British. We’re too darned polite.

A long fragment of a poem about the battle is one of the earliest examples of the English language. Unfortunately, it doesn’t make much sense nowadays, but there is a feisty translation by a local schoolteacher, Wilfrid Berridge.

Northey is a major bird sanctuary. The National Trust describes it as the closest Essex comes to true wilderness. It’s stout shoes country (but there are loos).

Popular with Havering people, West Mersea has long been a seaside resort. It’s thought the Romans from Colchester holidayed here. A mosaic pavement from a Roman villa was discovered under the churchyard in 1730.

Head for the lonely parish church of East Mersea. A 19th century rector, the Reverend Sabine Baring-Gould, penned the words of a famous hymn, Onward Christian Soldiers. In 1871, the year Baring-Gould came to Mersea, the composer Arthur Sullivan gave it a stirring melody.

Alas, its theme, of the Church “marching as to war”, is the sort of message about religion that we don’t want in the modern world.

Cudmore Grove Country Park stretches around the eastern end of Mersea Island. You can look out across the Colne estuary to Brightlingsea, and upriver towards the small port of Wivenhoe.

Unlike other Essex islands, which are basically walled marshland, Mersea rises to a dizzy 70 feet above sea level. Its south-facing slopes even support a vineyard!

At Cudmore Grove, crumbling cliffs (not very big ones, mind you) contain fossils.

Mersea is linked to the Essex mainland by The Strood, the causeway covered at high tide. Built (or perhaps rebuilt) around 700 AD, it must have been the work of the East Saxon kings, rulers of Essex whose names we barely know today.

Access to Wallasea and Northey is free. There’s a charge for parking at Cudmore Grove. Dog-owners should check local regulations, and respect the birds.