He is well known to be the original architect of the Baptistry of Pisa, in Piazza dei Miracoli, as we can read in the sign he left inside the building, with the date 1152 :
MCLIII, MENSE AUGUSTI FUNDATA FUIT HAEC ECCLESIA
DEUSTESALVET MAGISTER HUIUS OPERIS
Although he did the original project, the present Baptistery was different from his idea. In fact, he constructed only the first part, the ground floor. The building was continued after his death by Nicola Pisano, a century after its foundation, and then completed by Giovanni Pisano. They changed many things in the final form of the building, that was intended to be simpler with no gothic cusps and no dome, just a small, and high, pyramidal roof. This was connected to the fact that he wanted to resemble the Anastasis in the basilica of the Holy Sepulchre in Jerusalem. Maybe Diotisalvi wanted to replicate his previous work of the church of Holy Sepulchre in Pisa, 40 years before.
Church of Santo Sepolcro in Pisa
The Church of Holy Sepulchre, was built in the first part of 12th century. There are proofs that it existed in 1113. The church has an octagonal shape and a pyramidal roof. Inside the belltower, there is a sign where Deustesalvet claims to be the fabricator, i.e. constructor of the building. The inside was meant to resemble the Holy Sepulchre in Jerusalem, while the outside was meant to resemble the Dome of the Rock, also in Jerusalem, wrongly called for a long time by Europeans "Mosque of Omar", because at that time it was believed to be the Temple of Solomon. There are many churches in Europe dedicated to the Holy Sepulchre in octagonal or circular shape. We can cite the one in Bologna, Italy, inside the complex of Saint Stephen, or the one in Cambridge, or the Temple Church in London, United Kingdom.
Professional title
He was fabricator in 1113, and magister in 1153. That means he refined his art in some school, maybe the construction works of the cathedral of Pisa.
Other possible works
He did some other works, but without signing them.
Chapel of Saint Agatha
The chapel of Saint Agatha, a small chapel behind the church of Saint Paul a Ripa d'Arno. The small building was maybe originally built in 1063 by the monks, but the present shape was by a Diotisalvi. The first certification of the existence of the chapel is in 1132, maybe after the architect worked on it. It is in the usual octagonal shape, with a pyramidal roof.
The bell tower of the church of St Nicholas has an octagonal shape and a pyramidal roof, as all the other buildings by Diotisalvi. It was built in 1170, although there are no proofs, but only hypothesis. The bell-chamber instead is hexagonal with one window in every side. Inside there is a winding staircase, with a wall only on the external part, unlikely the Leaning Tower of Pisa. It was separated from the nearby buildings in origin, and it is slightly tilting.
Recent studies attribute by analogies also the famous Leaning Tower of Pisa to magister Diotisalvi. The shape, the construction, the affinity with the belltower of St. Nicholas all bring to the mindthe work of Diotisalvi. Like the Baptistery, the tower wasn't completed by him, maybe, just like the Baptistery, was Giovanni Pisano the last architect. That should explain why there is no pyramidal roof like all the other buildings.
