On the summit of An Cnap, a small hill north of Mid Sannox are the
remains of a vitrified fort. There are two subdued concentric
ramparts, now around 1m high, enclosing an oval area about 64m
north-south by 45m east west. The ramparts are most obvious on the
northern side and are absent to the east where steep slopes may
have offered protection and extensive views over the Firth of
Clyde. The southern part of the ramparts was excavated in the 1920s
and vitrified stone was found in the inner rampart. As the site is
now heavily overgrown with bracken it is difficult to find the
vitrified remains although the stone facing of the outer bank can
be seen over a short section on the north
side. The Sannox Fort is the only
vitrified structure on Arran, although to the west in Argyle they
are more common, such as the fort at Carradale overlooking
Kilbrannan Sound and the location of
Carra-Cache-1.
Vitrified forts are typical hill top
structures of the Iron Age in Scotland (900BC-500AD), but a few are
also found in Ireland and western France. Excavations in the 19th
century had shown that the ramparts of these forts were built from
a lattice of wood and stone and that high temperatures had caused
surface welding of the stones in the walls from a glassy melt.
Archaeologists in 1934 attempted to reproduce a vitrified rampart
by building a wall of refractory brick with a basalt rubble core at
colliery site near Stirling. Using brushwood they fired their wall
for three days at temperatures of over 1000°C during a snow storm,
but were only able to produce minor vitrification. However more
recent experiments using mica rich schists, typical of Northeast
Scotland and Argylshire, have produced vitrification by glassy
melts at around 850°C; a temperature
commonly achieved for 3 to 4 days in lime kilns.
Given the effort needed to vitrify the ramparts of a fort the
question then is why do it:
- Early antiquarians suggested that vitrification was a
deliberate technique to bind and strengthen the walls of the fort.
However vitrified walls are more brittle and less stable making
them easier to breach.
- Prior to to the experimental archaeological tests it was
thought that vitrification was carried out by an enemy to destroy
the stormed fort; they must of been pretty determined to haul the
volume of wood to the summit of a hill to fire the walls of the
fort for up to a week.
- Some archaeologists believe that vitrification is the
accidental consequence of iron making in bloomeries, as many forts
are quite small and may only have been used as cattle pens or
refuge sites in time of conflict.
- Probably the most widely held current theory is that
vitrification was the result of some ritual such as the cremation
of an important chief; the burning of a fierce fire on the hill top
that was the chief's power base which would cause its destruction
then becomes and important symbolic act.
The easiest route to the cache is from the car park at the
northern end of Sannox, by the stepping stones and opposite the
track into Glen Sannox. Follow the path over the river and then
northward along the shore passing the tall white navigation beacon.
As the path goes down the slope beyond the beacon a narrow path can
be followed westward across the marsh and then up onto An Cnap.
Alternatively those with a head for heights can carry on to the
large boulder at the base of the old sea cliff werea narrow
precipitous path goes up the face of the cliff,
this route is not suitable for
children; in wet weather
this path can be very slippery and as the path is on
the edge of a 30m vertical cliff the consequences of a trip would
be very serious.