In the Basilica of St John Lateran in the Middle Ages there have been many building projects, some of considerable scale, which are nonetheless not easy to identify. This chapter focusses on two examples, both of which give important insights into the building techniques employed: the lost front porch built by Pope Sergius II (844-847), which surviving illustrations indicate employed Carolingian construction technique typical for Rome, and the transept with the two bell towers attached to the northern side of the Basilica. In this second case the material evidence indicates both date of the building, in all probability from the pontificate of Nicholas IV (1288-1292), and its fine quality, appropriate to the exceptional importance of the project.