Within the reserve is the scheduled monument Tarr Steps, a clapper bridge over the River Barle. The name "clapper bridge" comes from the Medieval Latin "claperius" which means "pile of stones". It is an ancient form of bridge constructed with large unmortared slabs of stone resting on one another; this is the largest example of its type. There are 17 spans across 50 metres (55 yd), the top slabs weigh 1-2 tons and are about 39 inches (99 cm) above normal water level. The largest slab is over 8 feet (2.4 m) long and is about 5 feet (1.5 m) wide. This is one of the best known monuments on Exmoor. Its age is unknown, as several theories claim that Tarr Steps dates from the Bronze Age but others date them from around 1400 AD. It has been restored several times in recent years, following flood damage. Over the years the damage provides a good indicator of the strength of each flood. Some of the top slabs have been washed away in extreme flood conditions and they have now all been numbered to facilitate replacement.
The stones forming the spans weigh between one and two tons each and have on occasions been washed up to 50 yards (46 m) downstream. A distinctive feature of Tarr Steps is the slabs that are raked against the ends of each pier to break the force of the river and divert floating debris. Despite this, much of the damage has been due to debris such as branches floating down with the flood and battering the bridge. Debris used to be removed once a year by farmers from the Dulverton and Hawkridge sides of the river but since the flood of 1952 it has been trapped by cables strung across the river upstream of the bridge.
The bridge was badly damaged by floodwater on 22 December 2012 when steel wires upstream (designed to protect the bridge from damaging debris) were broken by fallen trees washed down the river. Floodwaters carried away part of the bridge again on 21 November 2016, and it has since been rebuilt.
Ian