Cassar's date of birth is not known, but he is believed to have been born in around 1520 in either
Birgu or
Gudja. The Cassar family, probably originating from
Sicily, had been established in Malta since at least the year 1440. He had two brothers, named Andreas and Ians, and married his wife Mathia in the early 1560s after which they had five children -two boys,
Vittorio and Gabriele; and three girls, Marietta, Battistina and Caterinella. Cassar had another child, Gio Domenico, from an extra-matrimonial relationship which he made sure to inherit none of his will and testament, ironically justifying himself by writing that his son was disobedient. Cassar was initially a
capomastro (master builder), and he was a pupil of
Evangelista Menga, the resident engineer of the
Order of St. John. He worked as a military engineer during the
Battle of Djerba in 1560 and the
Great Siege of Malta in 1565. During the latter siege, he worked on repairing fortifications damaged by the Ottoman assaults, sometimes at great personal risk. In 1566, the Order decided to construct a new capital city
Valletta, and Cassar became the assistant of
Francesco Laparelli, the Italian military engineer who had been sent to design the
city's fortifications and
grid plan. On 22 April 1569, Cassar was received within the Order in recognition of his merits as an architect and engineer. At this point, the Grand Master issued him a passport and Cassar spent the rest of the year touring Italian cities, , the only auberge which still retains Cassar's original design, with the only addition being a 19th-century
portico Upon his return to Malta in around late 1569, work on the Valletta fortifications was almost completed, and he took over the project after Laparelli left the island. He also became the Order's resident architect and engineer. He designed many public, religious and private buildings within the city, including the
Grandmaster's Palace, the seven original
auberges and the Conventual Church of St. John (now known as
St John's Co-Cathedral). Cassar also designed a few buildings outside the capital city, most notably the
Verdala Palace in
Buskett. The date and circumstances of Cassar's death are not recorded. He made his second will on 9 January 1589. He is believed to have died in around 1592 in Valletta. He was buried in the
Church of Porto Salvo in the same city. ==Buildings attributed to Cassar==