A bone anchoring device comprising: an anchor comprising a connection head and a bone anchoring part for fixation to a bone, a receiver, the receiver defining an axial direction, a radial direction and a circumferential direction, the receiver having a top portion defining a first end of the receiver and a base defining a second end of the receiver, the base having a seating surface defining a cavity, the cavity communicating with the exterior of the receiver through a first opening at the second end of the receiver, the seating surface having a seating cross sectional dimension larger than a first opening cross sectional dimension of the first opening, a retainer comprising at least two discrete retaining members (101, 102), each retaining member defining a mating surface corresponding to a portion of an outer surface of the connecting head, the retainer positionable around a lower portion of the connection head to form a first assembly having a first diameter smaller than the first opening cross sectional dimension such that the first assembly can be bottom loaded into the receiver by passing through the first opening, the retaining members having an outer surface formed to engage with the receiver seating surface once positioned within the receiver, an insert dimensioned to be received within the receiver through a first internal passage, the insert comprising a main body having a proximal surface forming a U-shaped saddle, and at least two pins (141, 142) protruding distally from the main body, each pin (141, 142) arranged to be inserted circumferentially between two adjacent retaining members (101, 102) of the retainer, so as to hold the retaining members (101, 102) circumferentially spaced apart from each other by insertion of the pin(s) (141, 142) therebetween to force the retaining members into an orientation creating a second diameter, larger then the first diameter, such that the outer surface of each retaining member engages the seating surface, thus securing the retaining members inside the cavity. an anchor comprising a connection head and a bone anchoring part for fixation to a bone, a receiver, the receiver defining an axial direction, a radial direction and a circumferential direction, the receiver having a top portion defining a first end of the receiver and a base defining a second end of the receiver, the base having a seating surface defining a cavity, the cavity communicating with the exterior of the receiver through a first opening at the second end of the receiver, the seating surface having a seating cross sectional dimension larger than a first opening cross sectional dimension of the first opening, a retainer comprising at least two discrete retaining members (101, 102), each retaining member defining a mating surface corresponding to a portion of an outer surface of the connecting head, the retainer positionable around a lower portion of the connection head to form a first assembly having a first diameter smaller than the first opening cross sectional dimension such that the first assembly can be bottom loaded into the receiver by passing through the first opening, the retaining members having an outer surface formed to engage with the receiver seating surface once positioned within the receiver, an insert dimensioned to be received within the receiver through a first internal passage, the insert comprising a main body having a proximal surface forming a U-shaped saddle, and at least two pins (141, 142) protruding distally from the main body, each pin (141, 142) arranged to be inserted circumferentially between two adjacent retaining members (101, 102) of the retainer, so as to hold the retaining members (101, 102) circumferentially spaced apart from each other by insertion of the pin(s) (141, 142) therebetween to force the retaining members into an orientation creating a second diameter, larger then the first diameter, such that the outer surface of each retaining member engages the seating surface, thus securing the retaining members inside the cavity.