Letocetum is the ancient remains of a Roman settlement. It was an important military staging post and posting station near the junction of Watling Street, the Roman military road to north Wales, and Icknield (or Ryknild) Street (now the A38). The site is now within the parish of Wall, Staffordshire, England. It is owned and run by the National Trust, under the name Letocetum Roman Baths Site & Museum. The site is in the guardianship of English Heritage as Wall Roman Site.

The Romans came to Letocetum in 50AD to establish a fortress during the early years of the invasion of Britain. The land could not support large numbers of soldiers and Letocetum, at an important cross-roads, became a large scale posting station. The settlement developed with successive bath houses and mansiones built to serve the official travellers as well as the growing civilian population. It is known mainly from detailed excavations in 1912–13, which concentrated on the sites of the mansio and bath-house.

The remains visible today are those of the stone bath house and mansio, built in approximately 130AD after Letocetum ceased to have a military function and became a civilian settlement. The settlement reached its peak during the 2nd and 3rd centuries and at this time occupied 8.1–12 hectares (20–30 acres). At the end of the 3rd century, the town relocated within high defensive walls astride Watling Street. After the Romans left early in the 5th century the settlement went into decline. The modern village of Wall emerged in the land once occupied by Letocetum.

The site is mentioned as Etocetum in the Antonine Itinerary and presumably represented a Latinisation of a Brittonic place name reconstructed as *Lētocaiton ("Grey-wood"; cf. Old Welsh: Luitcoyt and modern Welsh Lwytgoed ). The name possibly represented the species of tree prominent at the site such as ash and elm. Ford identifies the community as the Cair Luit Coyd ("Fort Greywood") listed by Nennius among the 28 cities of Britain in his History of the Britains.

It is likely that a small native settlement occupied the site before the advent of the Romans, possibly as the main trading station on the boundary between two British tribes, the Corieltauvi in the East Midlands whose later tribal centre was at Ratae Corieltauvorum, and the Cornovii to the west with their original capital Uriconon (which would later give its name to the important Roman British city of Viroconium) at the hill fort on The Wrekin. These tribes offered little resistance to Roman rule.

In about 50AD, a Roman vexillatio built a large timber fortress on a hilltop (near the site of the current church) at Letocetum. This housed the Legio XIV Gemina during the campaigns of governor Aulus Didius Gallus against the Brigantes. It was a good defensive position, but the poor farmland surrounding the fortress could not support large numbers of soldiers. During the Neronian period this initial fortress was replaced with a smaller one and Letocetum then developed into a large-scale posting station. Most of the troops moved to the fortress at Viroconium during the early administration of Gaius Suetonius Paulinus in about 58AD.

A mansio was built to provide lodging for official couriers travelling on Watling Street. A bath house was also built for the travellers and the growing civilian population. When the first mansio and bath house were completed, workers were needed to provide wood for the bath house, look after animals, and repair vehicles to be used by the official travellers. The civilian population would have provided many of these services. The native settlement grew during the Flavian period onwards to occupy 8.1–12 hectares (20–30 acres). Roman burials with 1st and 2nd century pottery were found along Watling Street in 1927, and more in 1966. In the field between the mansio site and Watling Street, a round depression in the ground may mark the site of a Roman amphitheatre or a circular gyrus for training horses (an example has been excavated at the Lunt Roman Fort). A large earthenware vessel in the likeness of Minerva was found near the modern church, which may therefore be the site of a temple of Minerva. A rectangular crop-mark in the field to the north-west of the bath-house, only visible in dry weather, may be the site of another temple.

When the Legion XIV first settled at Letocetum they would have used existing trackways. A stone-surfaced road was needed to allow reliable movement. Watling Street was given a stone surface past Letocetum in about 70 CE. This date is approximated from two coins found in the centre of Letocetum beneath the first road surfacing. There is no evidence to indicate when Ryknild Street was constructed, but from the layout it is thought that Watling Street was built first. Watling Street stretched from Letocetum to London in one direction and to Wroxeter and Chester in the other. Ryknild Street, 7.3 metres (24 ft) wide where it crossed with Watling Street, connected Letocetum with Cirencester to the south west and Yorkshire to the north east.