The amphitheatre was built outside the circle of walls
, next to the north gate, for obvious practical and functional reasons: in the second half of the Ist
century a.D., when the town was already three centuries old, it would have indeed been rather difficult to fit a building of such proportions within an already well established layout; what is more, its position outside the town favoured the access of a great number of spectators arriving both from the town and from the surroundings.
The building, measuring approximately 107 x 79 m. at its widest, rested upon a massive cement base that had been laid out on the entire surface to reinforce the alluvial ground. It was an elliptical ring, divided into 55 rooms, commonly referred to as "wedges". These rooms, placed on two levels and covered with progressively inward sloping vaults, supported the "cavea", i.e. the stands around the arena, where the spectators were seated, reached through internal flights of stairs. Open on the outside, these wedges appeared externally as a sequence of pillars and arches 3,80 m wide and divided into two orders: the lower one had 6,60 m. high arches, whereas the upper only 4,85 m.; the total height was over 13 metres. A low brick gallery, attested by 19th
century excavations, closed the wedges internally and defined the space of the arena (67 x 39 m.). The walls were made of concrete, with a plain brick face for the pillars of the lower order and one of white limestone ashlars, alternating with bands of brick, for those of the second order and for the walls of the single wedges. The seam between the two orders, as well as the arched lintels, were also of brick; the latter rested upon moulded stone lists.
The lower rooms, paved with large stone slabs, could be used as secondary entrances or utilities. There were at least two main entrances, at the ends of the major axis of the ellipse. We can still see part of two side pillars, made out of large hewn blocks, at the eastern gate, the only one remaining, opened according to Nottolini's project; upon the cornices we can observe, at the centre, two smaller cornices in low relief; in correspondence of these there were two pilasters, barely visible on the first bricks of the pillars. Evidently, this decoration, as that of the pillars themselves, was never quite completed.
At the eastern entrance, to the left, we can observe different masonry techniques, used in the course of time to close the fornixes: in particular, next to the pillars of the second order, simple cobblestone masonry, certainly older than the one in brick, was employed.
On the whole, Lucca's amphitheatre is simple and functional in its architecture; it lacks an external, ring shaped corridor and even the external decorations are nothing more than simple stone cornices. The fact that the building was never completely finished, as well as the need for the support of a wealthy citizen, show that the town was financially hard pressed in achieving this challenging construction. By the following century signs of the economic crisis were already evident in the loosening and decay of the urban fabric.