The chronological datings of 754 and 1284, referred to by the local historical sources for the start of building being recognised as unfounded, there are more correctly distinguished four phases in the development of the tower's construction: the first one, going back to the third decade of the 13th century, up to the third string-course cornice; a second phase in 1250-1267, up to the great cornice below the quadruple lancet window; a third, around 1284, as a coupling for the fourth phase, represented by the marble spire finished by 1309. Apart from the derivation of the typical Lombardy Romanesque tradition, also well in evidence in a Cremonese version, in the bell tower of S. Agata, of the second half of the 12th century, the Torrazzo has been proposed as a "type" of architecture new to Lombardy, the tower-spire, which was developed between the end of the 1200s and the early 1300s. Its inspirational source is the Lombardy, Romanesque dome covering and particular tower originating in Burgundy (end of the 12th century) in a harmonic fusion; implications to which there could be added an affinity between the Cremonese monuments and some towers of the Moorish-influenced Christian world. The Torrazzo, too, like other examples in Lombardy, including the facade of the duomo of Cremona in the phase of the early 14th century, reflects a significant change in taste expressed mainly in the modulation of the walls, substantially pictorial rather than architectural. In this sense the animation of the walls in terms of chiaroscuro is obtained through incisions with wide ogival mullioned windows with two or three lights and by resorting to slender vertical profiles or to horizontal cornices; elements, moreover, liberally arranged and without stringent structural limitations, making use of the best qualified channels of Cremonese brickworking techniques, above all in relation to spectacular proportions (111 metres in height). The marble crown, characterised by exquisite decorative elements, complete in chromatic terms and in lighting technique with its shaft in double-walled brickwork, giving it a conspicuous ascensional emphasis, further underlined by the octagonal two-layered spire and by its vertically narrowing width. The great astronomical clock constitutes the results of operations following the construction of the medioeval architectural structure: the exterior structure was originally painted by Paolo Scazzola in 1483 and was repainted many times by, among others, the painter G. Battista Natali in 1671, up to the present display dating back to 1974; the clock mechanism, however, is still the original, finished by Francesco Divizioli in 1583.