Have you seen or used the Montessori Roman Arch? It's simply beautiful but it's also really educational!
The Roman Arch is a block set which allows the child to use and learn Roman engineering principles to build an arch that seemingly defies gravity. It provides a really good introduction to Roman history, ancient architecture, principles of the keystone and the form and function of the arch.
This is a self-correcting, sensorial material that requires concentration and use of fine motor skills. Building the arch can be an individual or group activity and it's something that my children are instantly drawn to!
The child uses the individual blocks with the building support in place to form the arch. The blocks need to be placed in the correct sequence, this requires skill and is a real hands-on way to learn about this wonderful structure.
The moment of truth (and excitement) comes when you remove the building supports and the arch stands on its own!