Compared with other lands this far from the midday sun, the island is relatively warm. The reasons for this are not known, but suggest Britannia faces more out westerly into the ocean than some maps indicate, tucking in beside Hispania (Spain). Though visitors from sunnier places find it very cold under the stars of the Great Bear.
There are four main seasons, during all of which rain is a persistent menace. The sky is permanently hidden by clouds.
Experts who have measured these things declare that in the far north in particular, days here are longer than in Rome. There is light in the night time, since there is nothing to obstruct light from still reaching the high sky in these flat and empty parts, and in the furthest north but a slight difference between night and dawn at all as you watch the sun neither rise nor set but merely travel across the sky.
Temperatures vary from hot to cold. In the summer months, ensure when travelling you have enough liquids, ie stop to replenish your water skins when passing streams. In winter, particularly the exposed terrain in the north, the winds can get very biting. Snow can fall in some quantity. Not for nothing do some call it the island “rigid with ice and cold, far removed from both lands and the visible sun.” However, the land is spared the worst extremes of northern frosts.
Happily, the more established buildings have what is known as central heating. Gaps are left under the floors and in the walls for heated air to circulate, thus increasing room temperature. If you go and have a look how they do it, you might spot a local oddity. There is a type of marvellous black rock dug out of the ground locally that catches flame and burns with a ruddy glow giving off heat, and this is sometimes used.
Strong winds, storms, and lightning can be encountered. Fortunately, there are a large number of shrines and altars that can be used to keep the gods happy for when you are out and about.
Note that for repeat visitors, you may notice a change over time. In terms of temperature, you might spot a tiny increase around AD 300, then a gently sliding drop. You may find increased rainfall in the fifth century, leading to increased risks of flooding and difficulties travelling. You might also observe a drop in general temperature, and an increased level of public anger in general as they become seasonally depressed more easily, such as if crops fail. At the same time, you may over the long years also notice the sea level going up by several feet. Some talented sorcerers have calculated a rise of over two feet a century from the moment the Romans appear, perhaps thirteen feet over the whole period of empire, meaning extra earth and levels of props that keep needing to be added to water fronts and coastal roads.
Of course, such predictions may be alarmist. But they might explain why you need to take a bigger step off the boat next time you’re in harbour. Just be aware of the possible dangers your pillaging can have on the environment. Think of all those flooded coastal communities back home you’re forcing to up sticks and move into Roman lands. Have a social conscience. Try a smoke-free sacking. Take the ‘burn’ out of slash and burn.
That outdoorsy feeling: air vents like these keep Roman buildings free from barbarous odours
from The Discerning Barbarian's Guidebook to Roman Britain: People to Meet and Places to Plunder [Paperback] by Lee Rotherham