Lewis or Lewis Bolt or Lewis Key

The Lewis is a masonry stone lifting device, which in combination with a wooden crane, has been in existence for 2500 years.  No ancient Lewis, made entirely from iron, has survived the passage of time however, but it's tell-tale receptacle which is a Lewis hole carved into heavy cut stone has survived.

The appearance and mode of operation of the Lewis is best understood with the assistance of the illustration.  The Lewis is in three parts and consists of two wrought iron dovetail shaped parts and one (or more) plain wrought iron spacer.  The two dovetail parts were placed back to back in the diverging slot, previously chiseled out from the center of the stone block.  The internal dimensions of a typical Lewis Hole are determined based on the size of the Lewis. The spacer located between the two dovetailed parts results in filling the cavity of the Lewis hole.  A pin, assembled through a hole pierced through the top of the complete combination fixes the shackle to the Lewis.  The assembly is attached to hook, rope, and crane.  This enables the crane to manipulate the stone into position.  The essential issue is the Lewis tightening in the cavity.  The stone coming to rest releases the tension in the rope and the Lewis slackens in the taper of the hole allowing the assembly to be dismantled and the procedure repeated on the next stone block.

Some interesting examples of the known use of the lewis by the Romans include the construction of the coliseum in Rome, which was completed in 80 BC; the construction of the amphitheatre in Pompeii, which was commenced in 70 BC; and the construction of the temple at Baalbek from about 60 AD until about 250 AD.  Baalbek is of special interest, because the size and weight of many of the larger stones in the Temple of Jupiter, the first of the Roman temples that was constructed there, necessitated the use of multiple anchorages to enable them to be lifted and placed into position.  Several examples of stones that have multiple anchorages are easily found among the ruins of Baalbek.

The Romans introduced the lewis into Britain for the construction of Hadrian's Wall around 200 AD, when it was erected to prevent the incursions from Scotland into England.  You can still find mortises in many of the more massive stones in the ruins of Hadrian's Wall.  Later, the Saxons used the Lewis when they constructed the abbey at Whitby in 657 AD to accommodate the monks and nuns.